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Comparative morphology of selected aspects of the alimentary system of three species of limpets, Collisella… Latta, Lesley 1978

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COMPARATIVE MORPHOLOGY OF SELECTED ASPECTS OF THE ALIMENTARY SYSTEM OF THREE SPECIES OF LIMPETS, COLLISELLA PELTA 0RATHKE), C. PERSONA (RATHKE) AND C. SCUTUM (RATHKE). by LESLEY LATTA B . S c , U n i v e r s i t y o f B r i t i s h Columbia, 1975 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n THE FACULTY OF GRADUATE STUDIES (Department of Zoology) We accept t h i s t h e s i s as conforming to the r e q u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA February, 19 73 (g): L e s l e y L a t t a , 19 7 3 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of Brit ish Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of Zoology The University of Brit ish Columbia 2075 W e s b r o o k P l a c e V a n c o u v e r , C a n a d a V6T 1W5 Date M a r c h 10, 1978 ABSTRACT The morphology of the a l i m e n t a r y system was i n v e s t i g a t e d i n three s p e c i e s o f C o l l i s e l l a , (C. p e l t a , C. persona, and C. scutum). The r a d u l a r t e e t h were s t u d i e d u s i n g the scanning e l e c t r o n microscope. The t e e t h o f the above three s p e c i e s c o u l d be d i s t i n g u i s h e d by the a n t e r i o r c u r v a t u r e , antero-p o s t e r i o r and/or l a t e r a l i n c l i n a t i o n , sharpness o f the t i p s , and presence or absence o f u n c i n i . Wear p a t t e r n s o f the r a d u l a r t e e t h were s i m i l a r i n the three s p e c i e s . The r a d u l a r b a s a l p l a t e s c o u l d be d i f f e r e n t i a t e d by the a n t e r i o r l o b e , shape o f the p o s t e r i o r margin, o u t l i n e o f the o v e r l a p p i n g p l a t e s , and spacing o f p l a t e s along the r a d u l a r r i b b o n . Length and l o o p i n g o f the r a d u l a r sheath was i n v e s t i g a t e d . In C. persona the r a d u l a r l e n g t h ( r e l a t i v e to body s i z e ) was g r e a t e s t and the l o o p i n g the most complex. In C. p e l t a the the r a d u l a was s h o r t and l o o p i n g simple. C. scutum was in t e r m e d i a t e i n r e l a t i v e r a d u l a r l e n g t h and l o o p i n g . V a r i a -t i o n i n r a d u l a r l o o p i n g was determined by a comparison of 60 i n d i v i d u a l s o f each s p e c i e s from three d i f f e r e n t popula-t i o n s (20 o f each s p e c i e s from three d i f f e r e n t l o c a l i t i e s ) . S.E.M. micrographs o f the jaw showed t h a t i n C. p e l t a the a n t e r i o r band bore a median t o o t h , and v e n t r a l grooving due to the r a d u l a was deep and d i s t i n c t . In C. scutum the a n t e r i o r band of the jaw was o f t e n i r r e g u l a r , and v e n t r a l grooving was f a i n t . The jaws of C. persona had smooth a n t e r i o r bands, and the v e n t r a l s u r f a c e was unmarked. While l o o p i n g o f the i n t e s t i n e d i f f e r e d s l i g h t l y among the three s p e c i e s , c o n s i d e r a b l e i n d i v i d u a l v a r i a t i o n and some s p e c i e s . o v e r l a p was observed. Stomach diameter was l a r g e r i n C. p e l t a than i n the o t h e r two s p e c i e s . The placement of the p r o v e n t r i c u l u s r e l a t i v e to the stomach and p o s t e r i o r esophagus d i f f e r e d i n the three s p e c i e s . The s a l i v a r y glands were much l a r g e r i n C. p e l t a than i n C. scutum and C. persona. D i g e s t i v e gland tubules were acinous i n C. p e l t a , but t u b u l a r i n shape i n C. scutum and C. persona. The h i s t o l o g y o f the gut e p i t h e l i u m and a s s o c i a t e d glands was s t u d i e d u s i n g s e r i a l s e c t i o n s from 14 animals. No d i f f e r e n c e s among the three s p e c i e s were found. Morphology o f the above s t r u c t u r e s was c o n s i d e r e d with r e s p e c t to the r e p o r t e d d i e t o f each s p e c i e s . A c o r r e l a t i o n was found between r a d u l a r t o o t h form and the s p e c i e s r e p o r t e d p r e f e r e n c e f o r e i t h e r m i c r o s c o p i c algae o r macroscopic algae. The c o r r e l a t i o n was c o n s i d e r e d to be i n d i c a t i v e o f d i e t a r y a d a p t a t i o n . The morphology of the r a d u l a r t e e t h and the o t h e r c h a r a c t e r s s t u d i e d (basal p l a t e s , jaw, s a l i v a r y glands) were d i s c u s s e d w i t h r e s p e c t to the a d a p t a t i o n o f each s p e c i e s to i t s p r e f e r r e d a l g a l d i e t . The c h a r a c t e r s i n v e s t i g a t e d were c o n s i d e r e d w i t h r e s p e c t to t h e i r taxonomic v a l u e . They were ranked a c c o r d i n g t o the degree o f i n d i v i d u a l v a r i a t i o n found, and ease o f determina-t i o n o f the c h a r a c t e r . i v TABLE OF CONTENTS Page T i t l e Page i A b s t r a c t i i Table o f Contents i v L i s t o f Tables v i L i s t o f F i g u r e s v i i Acknowledgements x v i I. I n t r o d u c t i o n . 1 I I . M a t e r i a l s and Methods 10 C o l l e c t i o n o f Animals 10 Examination o f the Radula 10 Examination of -the .'.Jawc 22 Gross Morphology o f the Gut 23 H i s t o l o g y and H i s t o c h e m i s t r y o f the Gut and A s s o c i a t e d Glands 25 Examination of F e c a l P e l l e t s 27 I I I . R e s u l t s 28 A. Morphology o f the Radula 2 8 1. The Radular Teeth 2 8 2. B a s a l P l a t e s o f the Radula 46 3. Mechanical Wear o f the Radula 61 4. C o n f i g u r a t i o n o f the Radula 69 5. Length o f the Radula 87 V TABLE OF CONTENTS - (Continued) Page B. Morphology of the Jaw 96 1. Shape of the A n t e r i o r Band 96 2. Grooving o f the V e n t r a l S u r f a c e . . . . . . . 97 C. Morphology of the Gut and Rel a t e d S t r u c t u r e s 106 1. Gross Morphology 106 i . Looping o f Gut 106 i i . R e l a t i v e S i z e o f the S a l i v a r y Glands 118 i i i . Morphology o f D i g e s t i v e Gland Tubules 121 2. H i s t o l o g y o f the Gut and A s s o c i a t e d Glands 134 D. F e c a l P e l l e t s 186 IV. D i s c u s s i o n 192 A. F u n c t i o n a l Morphology 192 B. ITaxonorriy. . 205 V. Summary........... 209 L i t e r a t u r e C i t e d . 211 LIST OF TABLES Table 1 Summary of the Morphology o f the r a d u l a r t e e t h ; A. Inner l a t e r a l s , B. Median l a t e r a l s , C. Outer l a t - -erals, D. U n c i n i . 2 Summary o f the morphology o f the b a s a l p l a t e s o f the r a d u l a . 3 Summary o f mo r p h o l o g i c a l c h a r a c t e r s of the a l i m e n t a r y system and t h e i r r e l a t i o n to r e p o r t e d d i e t . v i i LIST OF FIGURES  F i g u r e Page l a Scanning electron micrograph of the 14 radular teeth of C o l l i s e l l a persona, viewed from the anterior. The speci-men was c r i t i c a l point dried, and the teeth appear as they do in the undried condition. Magnification approximately 100X. lb Scanning electron micrograph of the 14 radular teeth of C. persona, viewed from the anterior. The specimen was a i r dried, and the d i s t o r t i o n e f f e c t s are evident i n the greater l a t e r a l i n c l i n a t i o n of a l l radular teeth. Magnification approximately 100X. 2a Scanning electron micrograph of the 16 radular teeth of C o l l i s e l l a scutum, viewed from the l e f t side. The speci-men was c r i t i c a l point dried. Magni-f i c a t i o n approximately 200X. Scanning electron micrograph of the 16 radular teeth of C. scutum, viewed from the l e f t side. The specimen was a i r dried. Note the posterior i n c l i n a t i o n of a l l l a t e r a l teeth. Magnification approximately 20OX. Scanning electron micrograph of the 18 radular teeth of C o l l i s e l l a pelta, viewed from the posterior. The speci-men was c r i t i c a l point dried. Magni-f i c a t i o n approximately 100X. 3b Scanning electron micrograph of the 18 radular teeth of C. pelta, viewed from the posterior. The specimen was a i r dried. Note the increased l a t e r a l i n -c l i n a t i o n of the median l a t e r a l s , and the concave arcs at the bases of the inner l a t e r a l s . Magnification approxi-mately 100X. 2b 3a Diagram o f a r a d u l a r segment o f C o l l i -s e l l a p e l t a showing the important f e a -t u r e s o f the l a t e r a l t e e t h . M a g n i f i c a -t i o n approximately 200X. Scanning e l e c t r o n micrographs showing d i f f e r e n t views of the r a d u l a of C o l l i s e l l a p e l t a ; (a) viewed a t an angle from the a n t e r i o r , (b) viewed from the l e f t s i d e , (c) viewed from the a n t e r i o r , (d) viewed from the p o s t e r i o r . M a g n i f i -c a t i o n approximately 100X. Scanning e l e c t r o n micrographs showing d i f f e r e n t views of the r a d u l a o f C o l l i -s e l l a scutum; (a) viewed a t an angle from the a n t e r i o r , (b) viewed from the l e f t s i d e , (c) viewed from the a n t e r i o r , (d) viewed from the p o s t e r i o r . M a g n i f i -c a t i o n approximately 100X. Scanning e l e c t r o n micrographs showing d i f f e r e n t views of the r a d u l a o f C o l l i s e l l a persona; (a) viewed a t an angle from the a n t e r i o r , (b) viewed from the l e f t s i d e , (c) viewed from the a n t e r i o r , (d) viewed from the pos-t e r i o r . M a g n i f i c a t i o n approximately 100X. Scanning e l e c t r o n micrographs showing d i f f e r e n t views o f the r a d u l a o f C o l l i s e l l a l i m a t u l a ; (a) viewed a t an angle from the a n t e r i o r , (b) viewed from the l e f t s i d e , (c) viewed from the a n t e r i o r , (d) viewed from the p o s t e r i o r . M a g n i f i c a t i o n approximately 100X. Diagram o f s e v e r a l r a d u l a r segments of C o l l i s e l l a p e l t a showing the b a s a l p l a t e s . The v e n t r a l p l a t e s are shaded. The segment at the top of the page shows the o u t l i n e o f the o v e r l a p p i n g d o r s a l and v e n t r a l p l a t e s . At the bottom o f the page a p a i r o f d o r s a l p l a t e s i s shown with the p o s i t i o n of the l a t e r a l t e e t h i n d i c a t e d w i t h dashed l i n e s . M a g n i f i c a t i o n a p p r o x i -mately 100X. Diagram of s e v e r a l r a d u l a r segments o f C o l l i s e l l a scutum showing the b a s a l p l a t e s . The v e n t r a l p l a t e s are shaded. The segment a t the top of the page shows the o u t l i n e of the o v e r l a p p i n g d o r s a l and v e n t r a l p l a t e s . At the bottom o f the page a p a i r of d o r s a l p l a t e s i s shown wi t h the p o s i t i o n o f the l a t e r a l t e e t h i n d i c a t e d w i t h d o t t e d l i n e s . M a g n i f i c a t i o n approximately 100X., Diagram o f s e v e r a l r a d u l a r segments o f C o l l i s e l l a persona showing the b a s a l p l a t e s . The v e n t r a l p l a t e s are shaded. The segment a t the top o f the page shows the o u t l i n e o f the o v e r l a p p i n g d o r s a l and v e n t r a l p l a t e s . At the bottom of the page a p a i r o f d o r s a l p l a t e s i s shown wi t h the p o s i t i o n o f the l a t e r a l t e e t h i n d i c a t e d with d o t t e d l i n e s . M a g n i f i c a t i o n a p p r o x i -mately 100X. Diagram o f r a d u l a r b a s a l p l a t e s showing the o u t l i n e s of the l e f t d o r s a l and v e n t r a l p l a t e s t o g e t h e r (column i ) , and the o u t l i n e o f each i n d i v i d u a l p l a t e , d o r s a l (column i i ) , and v e n t r a l (column i i i ) ; (a) C o l l i s e l l a scutum, (b) C o l l i s e l l a  persona, (c) C o l l i s e l l a p e l t a . The f i g u r e s are composites of approximately ten i n d i v i -d uals o f each s p e c i e s . M a g n i f i c a t i o n approximately 10OX. Scanning e l e c t r o n micrographs showing two d i f f e r e n t views of both worn and unworn p o r t i o n s of the r a d u l a o f C o l l i s e l l a p e l t a ; (a) unworn t e e t h viewed from the l e f t s i d e , (b) worn t e e t h viewed from the l e f t s i d e , (c) unworn t e e t h viewed from the a n t e r i o r , (d) worn t e e t h viewed from the a n t e r i o r . M a g n i f i c a t i o n approximately 100X. Scanning e l e c t r o n micrographs showing two d i f f e r e n t views of both worn and unworn p o r t i o n s o f the r a d u l a o f C o l l i s e l l a scutum; (a) unworn t e e t h viewed from the l e f t s i d e , (b) worn t e e t h viewed from the l e f t s i d e , (c) unworn t e e t h viewed from the a n t e r i o r , (d) worn t e e t h viewed from the a n t e r i o r . M a g n i f i c a t i o n approximately 100X. X Figure Page 15 Scanning electron micrographs showing two 68 d i f f e r e n t views of both worn and unworn portions of the radula of C o l l i s e l l a persona; (a) unworn teeth viewed from the l e f t side, (b) worn teeth viewed from the l e f t side, (c) unworn teeth viewed from the anterior, (d) worn teeth viewed from the anterior. Magnification approximately 100X. 16a Photograph of a specimen of C o l l i s e l l a 76 persona which has been dissected to show the configuration of the radular sheath within the v i s c e r a l cavity. The dorsal mantle, gonad, digestive gland and gut have been removed. Magnification approxi-mately 6X. 16b Photograph of the above specimen p r i o r to 76 dissection. A portion of the radular sheath i s v i s i b l e beneath the dorsal mantle. 17a Photograph of a specimen of C o l l i s e l l a scutum 78 which has been dissected to show the configu-ration of the radular sheath within the v i s -c e r a l cavity. The dorsal mantle, gonad, digestive gland and gut have been removed. Magnification approximately 6X. 17b Photograph of the above specimen p r i o r to 78 dissection. A portion of the radular sheath i s v i s i b l e beneath the dorsal mantle. 18a Photograph of a specimen of C o l l i s e l l a pelta 80 which has been dissected to show the configu-rat i o n of the radular sheath within the v i s -c e r a l cavity. The dorsal mantle, gonad, digestive gland and gut have been removed. Magnification approximately 6X. 18b Photograph of the above specimen p r i o r to 80 dissect i o n . The radular sheath i s not v i s i b l e beneath the dorsal mantle. 19 Composite diagrams of 10 individuals of 82 each species c o l l e c t e d from Bamfield showing the va r i a t i o n i n radular configu-ration; (a) C. persona p r i o r to dissection, (b) C. persona a f t e r removal of the viscera, (c) C. scutum p r i o r to dissection, (d) C. s^cutum aft e r removal of the viscera, (e) C. pelta p r i o r to dissection, (f) C. pelta ( x i Figure Page af t e r removal of the viscera. Magnifi-cation 1.5 to 5X. 20 Composite diagrams of 10 individuals of 84 each species c o l l e c t e d from Stanley Park showing the v a r i a t i o n i n radular configu-r a t i o n ; (a) C. persona p r i o r to dissection, (b) C. persona a f t e r removal of the viscera, (c) C. scutum p r i o r to dissection, (d) C. scutum a f t e r removal of the viscera, (e) C. pelta p r i o r to dissection, (f) C. pelta a f t e r removal of the viscera. Magnification 1.5 to 5X. 21 Composite diagrams of 10 individuals of each 86 species c o l l e c t e d from Bowen Island showing the v a r i a t i o n i n radular configuration; (a) C. persona p r i o r to dissection, (b) C. persona af t e r removal of the viscera, (c) C. scutum p r i o r to dissection, (d) C. scutum a f t e r re-moval of the visc e r a , (e) C. pe l t a p r i o r to dissection, (f) C. pelta a f t e r removal of the visc e r a . Magnification 1.5 to 5X. 22 Regression of radular length as a function of 93 wet weight of s o f t parts i n three species of limpets from Bowen Island, B r i t i s h Columbia. Each point represents an i n d i v i d u a l . • = C o l l i - s e l l a persona; o = C o l l i s e l l a scutum; • = C o l l i - s e l l a p e l t a . 23 Regression of radular length as a function of 95 s h e l l length i n three species of limpets from Bowen Island, B r i t i s h Columbia. Each point represents an i n d i v i d u a l . • = C o l l i s e l l a  persona; O = C o l l i s e l l a scutum; • = C o l l i s e l l a  p e l t a . 24 Scanning electron micrographs showing the 101 dorsal surface of the jaw. Magnification approximately 5OX. (a) C. pel t a , note the pronounced beak i n the median area of the anterior band, (b) C. scutum, the anterior band i s s l i g h t l y uneven, (c) C. persona, the anterior band i s smooth. 25 Scanning electron micrographs showing the 103 ventral surface of the jaw of C o l l i s e l l a  p e l t a . Note the deep grooving i n the cen-tre of the anterior band; (a) Magnification approximately 50X, (b) Magnification approxi-mately 100X. X l l F i g u r e Page 26 Scanning e l e c t r o n micrographs showing 105 the v e n t r a l s u r f a c e of the jaw. Magni-f i c a t i o n approximately 50X. (a) C. scutum, some f a i n t grooving i s e v i d e n t i n the median r e g i o n s , (b) C. persona, the s u r -face i s smooth and unmarked. 27a Photograph o f a specimen of C o l l i s e l l a 109 persona d i s s e c t e d to show a p o r t i o n o f the a l i m e n t a r y c a n a l . The esophagus, stomach and p o r t i o n s o f the i n t e s t i n e can be seen. M a g n i f i c a t i o n a p p r o x i -mately 5X. 27b Diagram o f the above photograph. 109 28 Diagrams showing the course o f the stom- 111 ach, i n t e s t i n e , and rectum i n each o f the three s p e c i e s . Exact placement and s i z e of loops i s s u b j e c t to v a r i a t i o n w i t h i n each s p e c i e s . The g e n e r a l trends are shown; (a) C. p e l t a , (b) C. scutum, (c) C. persona. 29 Diagrams showing the placement o f the 115 p r o v e n t r i c u l u s r e l a t i v e to the stomach and p o s t e r i o r esophagus i n each o f the three s p e c i e s ; (a) C. p e l t a , d o r s a l and v e n t r a l views; (b) C. scutum, d o r s a l view, (c) C. persona, d o r s a l view. 30 Diagram o f a specimen of C. p e l t a showing 12 3 the e x t e n t o f the s a l i v a r y glands. The r e s t o f the v i s c e r a have been removed. The s a l i v a r y glands are s t i p p l e d . Maxi-mum gland s i z e i s as drawn; minimum s i z e i s shown with d o t t e d l i n e s . M a g n i f i c a t i o n approximately 8X. 31 Diagram o f a specimen o f C. scutum showing 125 the e x t e n t of the s a l i v a r y glands. The r e s t o f the v i s c e r a have been removed. The s a l i v a r y glands are s t i p p l e d . Maxi-mum gland s i z e i s as drawn; minimum s i z e i s shown with d o t t e d l i n e s . M a g n i f i c a t i o n approximately 8X. x i i i F i g u r e Page 32 Diagram of a specimen o f C. persona showing 127 the e x t e n t of the s a l i v a r y glands. The r e s t o f the v i s c e r a have been removed. The s a l i v a r y glands are s t i p p l e d . Maximum gland s i z e i s as drawn; minimum s i z e i s shown w i t h d o t t e d l i n e s . M a g n i f i c a t i o n approximately 8X. 33 Diagrams of p o r t i o n s o f the d i g e s t i v e gland 131 showing the shape o f the t u b u l e s ; (a) C o l l i s e l l a p e l t a , (b) C o l l i s e l l a scutum and C o l l i s e i l a persona. 34a Photograph o f a p l a s t i c c a s t o f the a n t e r i o r 133 d i g e s t i v e t r a c t o f C o l l i s e l l a p e l t a . 34b Diagram of the above photograph. 133 35a Photograph of a c r o s s s e c t i o n o f the p r o x i - 142 mal i n n e r l i p e p i t h e l i u m o f C o l l i s e l l a p e l t a . Note the g o b l e t c e l l s (G) between the e p i -t h e l i a l c e l l s , and the: mucocytes (MU) o f the i n t e r i o r o f the l i p . M a g n i f i c a t i o n 1000X. Haematoxylin and e o s i n . 35b Diagram o f the above c r o s s s e c t i o n . 142 36a Photograph o f a c r o s s s e c t i o n through the 144 s u b l i n g u a l c a v i t y of C o l l i s e l l a p e l t a . Goblet c e l l s and mucocytes are l o c a t e d a t the extreme r i g h t and l e f t c o r n e r s o f the c a v i t y . M a g n i f i c a t i o n 266X. Haematoxylin and e o s i n . 36b Diagram of the above c r o s s s e c t i o n . 144 37a Photograph of a s e c t i o n through the r a d u l a r 149 sac of C o l l i s e l l a persona. M a g n i f i c a t i o n 116X. Haematoxylin and e o s i n . 37b Diagram o f the above c r o s s s e c t i o n . 149 38a Photograph of a c r o s s s e c t i o n through the 151 a n t e r i o r esophagus o f C o l l i s e l l a scutum. M a g n i f i c a t i o n 200X. Haematoxylin and e o s i n . 38b Diagram o f the above c r o s s s e c t i o n . 151 39a Photograph o f a c r o s s s e c t i o n through the 153 midesophagus of C o l l i s e l l a persona. Magni-f i c a t i o n 97X. Haematoxylin and e o s i n . x i v F i g u r e Page 39b D i a g r a m o f t h e above c r o s s s e c t i o n . 153 40a P h o t o g r a p h o f a c r o s s s e c t i o n t h r o u g h 163 t h e e s o p h a g e a l g l a n d o f C o l l i s e l l a  p e r s o n a . M a g n i f i c a t i o n 400X. Haema-t o x y l i n and e o s i n . 40b D i a g r a m o f t h e above c r o s s s e c t i o n . 163 41a P h o t o g r a p h o f a c r o s s s e c t i o n t h r o u g h t h e 165 p o s t e r i o r e s o p h a g u s o f C o l l i s e l l a p e r s o n a . M a g n i f i c a t i o n 370X. H a e m a t o x y l i n and e o s i n . 41b D i a g r a m o f t h e above c r o s s s e c t i o n . 165 42 D i a g r a m s h o w i n g t h e c o u r s e o f t h e i n t e s t i n e 167 i n C o l l i s e l l a p e r s o n a w i t h t h e f i v e h i s t o -l o g i c a l r e g i o n s ( i - v ) . B o u n d a r i e s o f t h e s e r e g i o n s a r e s i m i l a r l y l o c a t e d i n C o l l i s e l l a p e l t a and C o l l i s e l l a scutum. 43a P h o t o g r a p h o f a c r o s s s e c t i o n t h r o u g h 169 r e g i o n v o f t h e i n t e s t i n e o f C o l l i s e l l a  p e r s o n a . Note t h e b a s a l g l a n d c e l l s l o c a t e d between t h e b a s e s o f t h e e p i t h e l i a l c e l l s . M a g n i f i c a t i o n 964X. H e i d e n h a i n ' s I r o n H a e m a t o x y l i n . 43b D i a g r a m o f t h e above c r o s s s e c t i o n . 169 44a P h o t o g r a p h o f a c r o s s s e c t i o n t h r o u g h 179 s e c t i o n i v o f t h e i n t e s t i n e o f C o l l i s e l l a  p e l t a . N ote t h e c l a v a t e g l a n d c e l l s b e -tween t h e e p i t h e l i a l c e l l s . M a g n i f i c a t i o n 1400X. H e i d e n h a i n ' s I r o n H a e m a t o x y l i n . 44b D i a g r a m o f t h e above c r o s s s e c t i o n . 179 45a P h o t o g r a p h o f a c r o s s s e c t i o n t h r o u g h t h e 181 r e c t u m o f C o l l i s e l l a scutum. M a g n i f i c a t i o n 335X. H a e m a t o x y l i n a n d e o s i n . 45b D i a g r a m o f t h e above c r o s s s e c t i o n . 181 46a P h o t o g r a p h o f a c r o s s s e c t i o n t h r o u g h a 183 s a l i v a r y d u c t o f C o l l i s e l l a scutum. Mag-n i f i c a t i o n 590X. H a e m a t o x y l i n and e o s i n . 46b D i a g r a m o f t h e above c r o s s s e c t i o n . 183 Photograph of a cross s e c t i o n through the d i g e s t i v e gland t u b u l e s of C o l l i s e l l a  persona. M a g n i f i c a t i o n 6 5 5 X . Haematox-y l i n and e o s i n . Diagram of the above cross s e c t i o n . Photograph showing f e c a l p e l l e t s shed from C o l l i s e l l a persona. M a g n i f i c a t i o n approximately 13X. Photograph showing f e c a l p e l l e t s shed from C o l l i s e l l a scutum. M a g n i f i c a t i o n approximately 13X. Photograph shwoing f e c a l p e l l e t s shed from C o l l i s e l l a p e l t a . M a g n i f i c a t i o n approximately 13X. x v i ACKNOWLEDGEMENTS I would l i k e to thank my s u p e r v i s o r Dr. P.A. Dehnel f o r h i s a s s i s t a n c e and c o n s t r u c t i v e c r i t i c i s m d u r i n g t h i s study. I would a l s o l i k e to thank Drs. A. Acton and P. Ford f o r c r i t i c a l l y r e a d i n g the manuscript. I am f u r -t h e r indebted to Daphne Hards f o r her gre a t a s s i s t a n c e and advice concerning h i s t o l o g i c a l techniques, and to L a s z l o Veto f o r h i s advice concerning S.E.M., photography, and dark room techniques. Thanks are due a l s o to Dr. H i l d a Ching who o f f e r e d many h e l p f u l suggestions, and to Chad Thorp f o r h i s a s s i s t a n c e with the s t a t i s t i c a l a n a l y s i s . 1 I. INTRODUCTION More than 80 s p e c i e s of acmaeid limpets have been d e s c r i b e d , r e p r e s e n t i n g an almost worldwide d i s t r i b u t i o n . The P a c i f i c Coast limpets are d i s t r i b u t e d from the A l e u t i a n I s l a n d s t o South America. Along the North American c o a s t there are 26 known s p e c i e s (McLean, 1966), many of which have o v e r l a p p i n g d i s t r i b u t i o n s . These animals, c o l l e c t i v e l y , occupy a l l l e v e l s of the i n t e r t i d a l shore, from the s u b t i d a l zone through t o the s p l a s h zone. D i s t i n c t v e r t i c a l zonation of s p e c i e s i s f r e q u e n t l y found, although some (eg. C. p e l t a ) occupy many i n t e r t i d a l l e v e l s (McLean, 19 66). Limpets are found i n r e g i o n s which present widely v a r y i n g environmental c o n d i t i o n s , i n c l u d i n g open c o a s t to p r o t e c t e d waters, and high s a l i n i t y t o e s t u a r i n e areas. D i f f e r e n t s p e c i e s are found on d i f f e r e n t s u b s t r a t a , which may o f t e n be s p e c i e s s p e c i f i c . For example, C o l l i s e l l a i n s e s s a occurs on E g r e g i a , C. i n s t a b i l i s occurs on Laminaria a n d e r s o n i i , C. paleacea occurs on P h y l l o s p a d i x and C. asmi occurs on the s h e l l of Tegula f u n e b r a l i s and other s p e c i e s of marine gastropods. Other acmaeid s p e c i e s occur on a rock substratum or on wharf p i l i n g s . While some of these s p e c i e s demonstrate c o n s i d e r -a b l e m i c r o h a b i t a t s p e c i f i c i t y (eg. C. i n s t a b i l i s ) , o t h e r s have invaded a v a r i e t y of m i c r o h a b i t a t s and are capable of t o l e r a t i n g a wide range of environmental c o n d i t i o n s (eg. C. p e l t a - Kohn, 1958; McLean, 1966). W i t h i n a l l C o l l i s e l l a 2 s p e c i e s , but p a r t i c u l a r l y w i t h i n the e u r y t o p i c members, there i s c o n s i d e r a b l e i n t r a s p e c i f i c v a r i a t i o n . The e x t e n s i v e l a t i -t u d i n a l d i s t r i b u t i o n s , the i n v a s i o n of p r a c t i c a l l y every i n t e r t i d a l m i c r o h a b i t a t , and the marked p o p u l a t i o n v a r i a t i o n demonstrated by t h i s group, suggests t h a t adaptive r a d i a t i o n has played an important r o l e i n the success of these animals. M o r p h o l o g i c a l a d a p t a t i o n , or a t l e a s t v a r i a t i o n i n response to environmental c o n d i t i o n s , has been w e l l documented i n s h e l l c h a r a c t e r s ( R u s s e l l , 1907; Orton, 1928, 1929, 1933; Moore, 1934; Bonar, 1936; Grant, 1937; Hewatt, 1940; C u r t i s s , 1941; T e s t , 1945, 1946; McLean, 1966; Jobe, 1968; Rao and Ganapati, 1971; B a n n i s t e r , 1975). There are, however, no known s t u d i e s which r e p o r t m o r p h o l o g i c a l a d a p t a t i o n s or v a r i a t i o n of the i n t e r n a l anatomy among s p e c i e s . There i s , i n f a c t , a p a u c i t y of i n f o r m a t i o n r e l a t e d to s o f t - p a r t morphology i n l i m p e t s of the genus C o l l i s e l l a . Most of the e a r l y s t u d i e s were not comparative, and d e a l t w i t h the anatomy of one s p e c i e s (eg. W i l l c o x , 1901; 1906). I n v e s t i g a t i o n s of comparative morphology appear to be l i m i t e d t o three works. R i g h i (19 66) i n v e s t i -gated three s p e c i e s c o l l e c t e d from B r a z i l , F r e t t e r and Graham (1962) d e a l t with a few of the B r i t i s h s p e c i e s , and Walker (1968) r e p o r t e d aspects of a l i m e n t a r y morphology among s i x s p e c i e s c o l l e c t e d from the area adjacent to Monterey, C a l i f o r n i a . I t has been noted i n the few s t u d i e s undertaken on s o f t - p a r t morphology t h a t many of the c h a r a c t e r s by which s p e c i e s d i f f e r e d were r e l a t e d to the a l i m e n t a r y system ( R i g h i , 1966; Walker, 1968). D i f f e r e n c e s i n d i g e s t i v e mor-3 phology among C o l l i s e l l a s p e c i e s become important when viewed i n the c o n t e x t of d i e t a r y a d a p t a t i o n . The present study i n d i c a t e s a c o r r e l a t i o n (among C o l l i s e l l a p e l t a , C. scutum, and C. persona) between r a d u l a r t o o t h form and the r e p o r t e d p r e f e r e n c e of the s p e c i e s f o r e i t h e r m i c r o s c o p i c algae ( u n i c e l l u l a r a l g a l f i l m s ) or macro-s c o p i c algae ( s t i p e or fronds of seaweeds). The c o r r e l a t i o n i s s u g g e s t i v e of d i e t a r y a d a p t a t i o n . T h i s study, t h e r e f o r e , examines s e l e c t e d aspects Of the a l i m e n t a r y system among the above three C o l l i s e l l a s p e c i e s . Species d i f f e r e n c e s i n these s e l e c t e d aspects are c o n s i d e r e d i n terms of the r e p o r t e d p r e -valence of e i t h e r m i c r o s c o p i c or macroscopic algae i n the d i e t s of these animals. The three s p e c i e s s t u d i e d occupy the mid to h i g h i n t e r t i d a l h a b i t a t . They t y p i c a l l y occur on a rock sub-stratum, but there i s a v a r i a n t form of C. p e l t a which occurs on the s t i p e of E g r e g i a (McLean, 1966; P r o c t o r , 1968; C r a i g , 1968; Smith and C a r l t o n , 1974). Other v a r i a n t forms of C. p e l t a have been d e s c r i b e d (McLean, 1966). McLean (1966) has d i s c u s s e d d i s t r i b u t i o n s and ecology f o r each of these s p e c i e s . Aspects of r a d u l a r morphology were s e l e c t e d f o r comparative i n v e s t i g a t i o n i n the three s p e c i e s . The l i t e r a -t u r e l a c k s adequate documentation of the r a d u l a r t e e t h i n C o l l i s e l l a s p e c i e s . Sketches bf the t e e t h have been gi v e n by a few authors. These were made from c o n v e n t i o n a l p r e p a r a t i o n s i n which the t e e t h are f l a t t e n e d out by the c o v e r s l i p , and i n which o n l y d o r s a l views of the t e e t h are p o s s i b l e . W r i t t e n 4 descriptions have not c l a r i f i e d the c h a r a c t e r i s t i c s by which radular teeth of C o l l i s e l l a species d i f f e r . Sketches of the radular teeth of C. pelta are given by D a l l (1871), Odhner (1912), Curtiss (1941), Habe (1958) and Golikov and K u s s a k i n (1972, using the synonym C. c a s s i s ) . In a l l cases the teeth are shown in dorsal view only, except by Curtiss (1941) where p r o f i l e views also are given. In a l l cases the s p a t i a l relationships of the teeth are not documented adequately. These have been found i n the present study to be important i n distinguishing the radulae of d i f f e r e n t species. The same i s true for C. scutum, where the only published figure (Dall, 1871, using the synonym C. patina) i s incorrect. McLean (1966) suggests that Dall's i l l u s t r a t i o n may represent a composite of several individuals and species. The only correct figure of the radular teeth of C. persona i s given by Curtiss (1941). Again, Dall's (1871) figure i s incorrect as uncini are shown and the c h a r a c t e r i s t i c shape of the basal plates of C. persona i s not (McLean, 1966). There are, therefore, no (satisfactory) published i l l u s t r a t i o n s of the radular teeth of these species. There are no published or unpublished photographs of the radular.teeth of any C o l l i s e l l a species. In the present study, therefore, the radular teeth were investigated and documented with scanning electron micro-graphs. For purposes of comparison with the three species under study, an additional species with a documented feeding preference, C o l l i s e l l a limatula, was obtained from Corona Del Mar, C a l i f o r n i a , and investigated for radular tooth form using 5 the S.E.M. This species does not occur north of Oregon, U.S.A. (44°N l a t i t u d e , McLean, 1966). The form of C. pelta which i n -habits Egregia was obtained from Bamfield, Vancouver Island for S.E.M. study. The basal plates of the radula. are also i n v e s t i -gated. With the exception of Fritchman (1960b), who deals with only three species, there are no published accounts which describe and figure adequately the basal plates of C o l l i s e l l a species. Grant's (19 37) thesis with i l l u s t r a t i o n s and des-c r i p t i o n s of many species i s unpublished. Previous studies have shown that radular teeth are continually secreted at the posterior end by the radular bulb, move forward along a subradular membrane toward the anterior, and then are worn down and shed at the m o s t a n t e r -i o r end as contact i s made with the substratum (Piele, 1937; Fretter and Graham, 1962; Runham, 1962, 1963; Isarankura and Runham, 1968). Mechanical wear on the radular teeth has been reported for P a t e l l a vulgata (Runham and Thornton, 1967). The S.E.M. was used to reveal changes in surface morphology of the teeth along the ribbon brought about by t h e i r abrasion on the rock surface during the feeding process. No other s i m i l a r study on wear of the radular teeth i s known. Radular wear patterns were, therefore, investigated i n the three species. 6 Looping of the radular sheath through the v i s c e r a l mass was studied. Differing^ radular configurations among some species of C o l l i s e l l a have been noted b r i e f l y by pre-vious authors. Walker (1968) noted a longer and more poste-r i o r l y placed radula i n C. scutum than i n other C a l i f o r n i a n species studied. Righi (1966) noted an extra radular loop in one of the three B r a z i l i a n species investigated. F r i t c h -man (in I l l g , 1969) l i s t s the location of the radula d i r e c t l y beneath the dorsal mantle of the v i s c e r a l mass as a d i s t i n -guishing feature of C. persona. The course of radular looping in t h i s species has not, however, been figured or described. Radular looping patterns were, therefore, investigated i n the three C o l l i s e l l a species. Three populations were considered i n the investigation of t h i s character (Tunstall Bay, Bowen Island; Bamfield, Vancouver Island; Stanley Park, Vancouver). The length of the radula has been documented as a s p e c i f i c character for some species of C o l l i s e l l a (Righi, 1966; Walker, 1968) and for some species of P a t e l l a (Eslick, 1940; Evans, 1947; Koch, 1949; Brian and Owen, 1952; Ebling et a l , 1962). Radular length has also been reported i n Cellana radiata for animals located at d i f f e r e n t i n t e r t i d a l l e v e l s (Rao and Ganapati, 1967). In a l l of the above studies, the radular lengths were considered r e l a t i v e to s h e l l length, and i n a l l except the study of Cellana, figures on radular length were reported i n the form of the radular f r a c t i o n , which i s defined as: 7 r a d u l a r f r a c t i o n = r a d u l a r l e n g t h (mm) s h e l l l e n g t h (mm) Thus, r a d u l a r l e n g t h s have been expressed as r a t i o s of s h e l l l e n g t h s , and o f t e n o n l y the mean r a d u l a r f r a c t i o n o f a sample was gi v e n . I t i s b e l i e v e d t h a t more i n f o r m a t i o n r e g a r d i n g the r a d u l a r l e n g t h i n r e l a t i o n to animal s i z e can be p r o v i d e d by p r e s e n t i n g the r e s u l t s g r a p h i c a l l y . In the presen t study r a d u l a r l e n g t h was p l o t t e d a g a i n s t wet weight of s o f t p a r t s and a g a i n s t s h e l l l e n g t h u s i n g measurements from the same sample i n each p l o t f o r the three s p e c i e s , C. p e l t a , C. per-sona, and C. scutum. D i f f e r e n c e s i n jaw shape have been documented among some B r a z i l i a n C o l l i s e l l a s p e c i e s ( R i g h i , 1966) and among some C a l i f o r n i a n s p e c i e s (Walker, 1968), p a r t i c u l a r l y i n the r e g u l a r i t y o f the median area o f the a n t e r i o r band. Walker (1968) found t h a t while i n some s p e c i e s the a n t e r i o r band was smooth and unridged, i n o t h e r s the margin was o f t e n s l i g h t l y r i d g e d o r bore a median t o o t h . Jaw shape was, t h e r e f o r e , i n -v e s t i g a t e d i n the three s p e c i e s . Grooving o f the v e n t r a l s u r f a c e o f the jaw was a l s o s t u d i e d . D i s t i n c t , w e l l - o r d e r e d jaw grooving has been r e p o r t e d i n P a t e l l a v u l g a t a (Runham and Thornton, 1967). The grooves are thought to be produced by the l a t e r a l and dominant t e e t h o f the r a d u l a , c o n f i r m i n g t h a t (as suggested by Graham, 1964) the r a d u l a and the jaw are pre s s e d c l o s e l y together d u r i n g r a d u l a r movements wh i l e the animal i s f e e d i n g . I t was thought t h a t , i f s i m i l a r grooving 8 i s produced i n C o l l i s e l l a species due to radula-jaw contact, the d i f f e r i n g morphology of the radular teeth i n the three species might produce d i f f e r i n g patterns of grooving i n the jaw. The anatomy of the gut and associated glands has been reported for several C o l l i s e l l a species (Righi, 1966; Walker, 1968). Walker (1968) found that while a general pattern of gut looping existed within the genus C o l l i s e l l a , each species showed d i s t i n c t trends i n loop size and place-ment. Gut morphology was considered i n the three species here studied. In addition, the histology of the gut epithelium and glands was studied with respect to i n t e r s p e c i f i c d i f f e r -ences. No previous investigations of comparative histology of the digestive system i n C o l l i s e l l a species are known. Characters of the s h e l l have been used as the primary c r i t e r i a for i d e n t i f i c a t i o n of limpet species. Con-siderable confusion has, however, resulted from sole depen-dence upon the s h e l l for taxonomic purposes. This i s , i n part, due to the extreme s h e l l v a r i a t i o n which i s produced by environmental factors. Due to the d i f f i c u l t i e s that e a r l i e r workers encountered i n i d e n t i f i c a t i o n of acmaeid species because of s h e l l v a r i a t i o n , long l i s t s of synonymys have resulted for each species, as well as numerous generic and subgeneric reorganizations (eg. D a l l , 1871; P i l s b r y , 1922; Oliver, 1926; Grant, 1937; McLean, 1966). For t h i s reason, the more recent c l a s s i f i c a t i o n schemes have included char-9 acters of the radular teeth and basal plates, since they are not subject to environmental v a r i a t i o n (Grant, 1937; Curt i s s , 1941; McLean, 1966; Fritchman, 1960b; MOskalev, 1966; Golikov and Kussakin, 1972). There remains, however, a lack of adequate documentation i n the l i t e r a t u r e of both the radular teeth and the basal plates i n C o l l i s e l l a species. The advantages of using the scanning electron microscope i n the study of gastropod radulae have been d i s -cussed (Runham and Thornton, 1967; Thompson and Hinton, 1968; Runham, 1969; Thompson and Bebbington, 1973). Hickman (1977) examined the advantages of integration of l i g h t and electron microscope studies of molluscan radulae. She has stated that more information on radular structure can be gained by u t i l i -zing S.E.M. preparations i n conjunction with the t r a d i t i o n a l l i g h t microscope methods. Further, she has stressed the fact that, due to the high resolving power, great depth of f i e l d , and the a b i l i t y to explore photomicrography from various , angles, the S.E.M. e f f e c t i v e l y demonstrates three dimensional morphology. Light microscope preparations provide information with regard to overlapping structures and staining patterns (Hickman, 1977). It i s believed that more complete documentation of radular structure i n C o l l i s e l l a species i s necessary i f the radular teeth are to be used for purposes of taxonomy. The present study on the radular teeth using the S.E.M. c o n t r i -butes toward t h i s needed information i n three species of th i s genus. 10 I I . MATERIALS AND METHODS C o l l e c t i o n o f Animals Most of the specimens examined i n the study were c o l l e c t e d from T u n s t a l l Bay, Bowen I s l a n d , B r i t i s h Columbia at two to three month i n t e r v a l s from September, 1975 to January, 1977. In a d d i t i o n , animals from two other l o c a l i t i e s (Bamfield Marine S t a t i o n , Vancouver I s l a n d , and Brockton P o i n t , S t a n l e y Park) were c o l l e c t e d f o r examination o f r a d u l a r con-f i g u r a t i o n . Specimens of C o l l i s e l l a l i m a t u l a from Corona Del Mar, C a l i f o r n i a , and of the E g r e g i a form o f C. p e l t a from Seppings I s l a n d near B a m f i e l d Marine S t a t i o n were o b t a i n e d f o r comparative scanning e l e c t r o n microscope s t u d i e s on the r a d u l a r t e e t h . Animals were h e l d i n separate tanks f i l l e d w i t h 21.5io seawater a t 10°C, and were kept i n darkness. They were not f e d . Examination of the Radula a. Scanning E l e c t r o n Microscope I n v e s t i g a t i o n P o r t i o n s of the r a d u l a from twenty animals each of C o l l i s e l l a p e l t a (rock d w e l l i n g form and E g r e g i a form), C. persona and C. scutum, and f i v e animals o f C. l i m a t u l a , were prepared by the f o l l o w i n g method f o r examination i n the Scanning E l e c t r o n Microscope (S.E.M.). The r a d u l a was b o i l e d i n 10% NaOH f o r approximately 30 minutes. T h i s procedure e f f e c t i v e l y d i s s o l v e d away the encasing membrane of the r a d u l a . The s t r u c t u r e was washed i n 11 s e v e r a l changes of d i s t i l l e d water and cut i n t o a p p r o x i -mately 5 mm l e n g t h s . The worn areas of the r a d u l a r r i b -bon (due to a b r a s i o n on the substratum), and the areas where the t e e t h were i n c o m p l e t e l y formed were d i s c a r d e d . The remaining p o r t i o n s of i n t a c t radulae were p l a c e d i n s t a i n l e s s s t e e l mesh baskets, dehydrated through an e t h a n o l s e r i e s (70%, 95%, and two changes of 100%), s u b s t i t u t e d with amyl a c e t a t e , and c r i t i c a l p o i n t d r i e d by the CCX, method (Anderson, 1951). The d r i e d p i e c e s of r a d u l a were mounted on aluminum stubs u s i n g a copper (conducting)tape w i t h the s t i c k y s i d e upwards. The edges of the tape were s e a l e d to the stub w i t h s i l v e r p a i n t . The stubs were coated w i t h g o l d u s i n g a Mikros vacuum evaporator. The reasons f o r g o l d c o a t i n g are d i s c u s s e d i n Runham and Thornton (1967). The coated stubs were examined i n a Cambridge Mark 2A s t e r e o s c a n . The radulae of f i v e specimens each o f C. p e l t a , C„ persona, and C. scutum were prepared f o r examination of the area e v i d e n c i n g t o o t h a b r a s i o n . P r e p a r a t i o n was as o u t l i n e d above, except t h a t o n l y the most p o s t e r i o r end o f the r a d u l a r r i b b o n ( l o c a t e d w i t h i n the b u c c a l c a v i t y ) was d r i e d and mounted. Extreme care was taken i n the mounting process i n order to prevent damage to the worn t e e t h , and y e t s t i l l e f f e c t good c o n t a c t between the specimen and the stub. Due to the f a c t t h a t t h e r e i s continuous replacement of the r a d u l a r t e e t h , the worn p o r t i o n o f the r a d u l a was soon shed i n l a b o r a t o r y h e l d 12 animals. In t h i s study, t h e r e f o r e , i t was necessary to d i s s e c t the radulae from the animals immediately a f t e r c o l l e c t i o n . I n i t i a l l y , some ra d u l a e , prepared f o r S.E.M. exami-n a t i o n of the t e e t h , were a i r - d r i e d and mounted as above. Whereas c r i t i c a l p o i n t d r i e d radulae were not a l t e r e d i n any way by the d r y i n g process, a i r - d r y i n g d i s t o r t e d the s p a t i a l r e l a t i o n s h i p s of the r a d u l a r t e e t h . The major e f f e c t was to push the t e e t h a p a r t so t h a t they assumed a more l a t e r a l i n c l i n a t i o n . T h i s e f f e c t was produced i n the i n n e r , median, and o u t e r l a t e r a l s , but the median l a t e r a l s , being the l a r g e s t i n s i z e , seemed to be the most a f f e c t e d ( F i g s , l a and l b ) . The second e f f e c t was t h a t of pushing the t e e t h p o s t e r i o r l y so t h a t the median and o u t e r l a t e r a l s assumed a p o s t e r i o r i n c l i n a t i o n , r a t h e r than t h e i r u s u a l a n t e r i o r i n c l i n a t i o n , ( F i g s . 2a and. 2b). The o u t e r l a t e r a l s , which are the s m a l l e s t l a t e r a l t e e t h , were pushed so f a r p o s t e r i o r l y t h a t they o f t e n l a y p a r a l l e l t o the r a d u l a r r i b b o n , and t h e i r a n t e r i o r s u r -f a c e s faced d o r s a l l y ( F i g s . 2a and 2b). In C. p e l t a the concave arc l o c a t e d a t the base of each median l a t e r a l t o o t h appeared much more pronounced i n a i r - d r i e d s p e c i -mens than i t d i d i n the c r i t i c a l p o i n t d r i e d or u n d r i e d c o n d i t i o n s ( F i g s . 3a and 3b). Concave a r c s were a l s o produced on the p o s t e r i o r face of the i n n e r l a t e r a l s a t the bases of the cusps. These were not found i n u n d r i e d or c r i t i c a l p o i n t d r i e d specimens. In C. persona, where F i g u r e l a . Scanning e l e c t r o n micrograph of the r a d u l a r t e e t h of C o l l i s e l l a persona, viewed from the a n t e r i o r . The specimen was c r i t i c a l p o i n t d r i e d , and the t e e t h appear as they do i n the u n d r i e d c o n d i t i o n . M a g n i f i c a t i o n approximately 100X. A, a n t e r i o r ; IL, i n n e r l a t e r a l t o o t h ; ML, median l a t e r a l t o o t h ; OL, o u t e r l a t e r a l t o o t h ; P, p o s t e r i o r . F i g u r e l b . Scanning e l e c t r o n micrograph of the r a d u l a r t e e t h o f C_. persona, viewed from the a n t e r i o r . The specimen was a i r d r i e d , and the d i s t o r t i o n e f f e c t s are e v i d e n t i n the g r e a t e r l a t e r a l i n c l i n a t i o n of a l l r a d u l a r t e e t h . M a g n i f i c a t i o n approximately 100X. A, a n t e r i o r ; IL, i n n e r l a t e r a l t o o t h ; ML, median l a t e r a l t o o t h ; OL, o u t e r l a t e r a l t o o t h ; P, p o s t e r i o r . F i g u r e 2a. Scanning e l e c t r o n micrograph of the r a d u l a r t e e t h of C o l l i s e l l a scutum, viewed from the l e f t s i d e . The specimen was c r i t i c a l p o i n t d r i e d . M a g n i f i c a t i o n approximately 200X. A, a n t e r i o r ; IL, i n n e r l a t e r a l t o o t h ; ML, median l a t e r a l t o o t h ; OL, outer l a t e r a l t o o t h ; P, p o s t e r i o r . F i g u r e 2b. Scanning e l e c t r o n micrograph of the r a d u l a r t e e t h o f C. scutum, viewed from the l e f t s i d e . The specimen was a i r d r i e d . Note the p o s t e r i o r i n c l i -n a t i o n o f a l l l a t e r a l t e e t h . M a g n i f i c a t i o n a p p r o x i -mately 200X. A, a n t e r i o r ; IL, i n n e r l a t e r a l t o o t h ; ML, median l a t e r a l t o o t h ; OL, ou t e r l a t e r a l t o o t h ; P, p o s t e r i o r . b F i g u r e 3a. Scanning e l e c t r o n micrograph of the r a d u l a r t e e t h o f C o l l i s e l l a p e l t a , viewed from the p o s t e r i o r . The specimen was c r i t i c a l p o i n t d r i e d . M a g n i f i c a t i o n approximately 100X. A, a n t e r i o r ; IL, i n n e r l a t e r a l t o o t h ; ML, median l a t e r a l t o o t h ; OL, outer l a t e r a l t o o t h ; P, p o s t e r i o r . F i g u r e 3b. Scanning e l e c t r o n micrograph of the r a d u l a r t e e t h of C. p e l t a , viewed from the p o s t e r i o r . The specimen was a i r d r i e d . Note the i n c r e a s e d l a t e r a l i n c l i n a t i o n o f the median l a t e r a l s , and the concave a r c s a t the bases o f the i n n e r l a t e r a l s . M a g n i f i c a t i o n approximately 100X. A, a n t e r i o r ; IL, i n n e r l a t e r a l t o o t h ; ML, median l a t e r a l t o o t h ; OL, o u t e r l a t e r a l t o o t h ; P, p o s t e r i o r . 19 the i n n e r l a t e r a l s are t a l l and narrow, the to o t h was o f t e n broken a t the p o i n t where the base j o i n s the cusp of the i n n e r l a t e r a l s ( F i g . l b ) . A i r - d r y i n g a l s o a f f e c t e d the r a d u l a r r i b b o n . The ri b b o n margins tended to curve v e n t r a l l y and the r i b b o n tended to form a s p i r a l curve along i t s l e n g t h . These d i s t o r t i o n s made even c o n t a c t between the v e n t r a l s u r f a c e of the specimen and the conducting tape much more d i f f i -c u l t to o b t a i n . The ribbons o f c r i t i c a l p o i n t d r i e d specimens were smooth and f l a t and, t h e r e f o r e , made b e t t e r c o n t a c t w i t h the stub. Thus, the problems of specimen c h a r g i n g and e l e c t r o n d i s c h a r g e i n c r i t i c a l p o i n t d r i e d specimens were reduced. L i g h t Microscope I n v e s t i g a t i o n Thick mounts were made of i n t a c t r a d u l ae (with t e e t h a t t a c h e d ) . Three specimens o f each s p e c i e s were prepared a f t e r the method of Fritchman (1960a), except f o r the f o l l o w i n g m o d i f i c a t i o n s . The t e e t h were not removed, but r a t h e r the e n t i r e radulae were s t a i n e d i n acetocarmine and dehydrated through a graded e t h a n o l s e r i e s to 100%, and r i n s e d i n xylene. They were mounted with a 1 mm t h i c k p l a s t i c r i n g u s i n g Permount, r a t h e r than E u p a r a l , as the mounting medium. Care was necessary i n order to ma i n t a i n the r a d u l a i n the d e s i r e d o r i e n t a t i o n while c o v e r s l i p p i n g . Some ribbons were s t a i n e d i n acetocarmine, and some i n c h l o r a z o l b l a c k E ( d i s s o l v e d i n 50% l a c t i c a c i d ) . Radular ribbons mounted i n t h i s manner 20 and viewed through a d i s s e c t i n g microscope r e v e a l e d the a s s o c i a t i o n between the t e e t h and the b a s a l p l a t e s , and p e r m i t t e d a three dimensional (stereo) view of the s t r u c t u r e without the squashing and d i s t o r t i o n which oc c u r r e d when i t was mounted w i t h a c o v e r s l i p i n the con-v e n t i o n a l manner. P o r t i o n s of the r a d u l a from ten animals of each o f the three s p e c i e s were prepared f o r demonstration o f the b a s a l p l a t e s . The same r e g i o n of the r a d u l a was prepared i n each animal, (the f i r s t ten to twenty post-odontophoral p l a t e s ) , as the p l a t e p a t t e r n has been r e p o r t e d to a l t e r along the r i b b o n (Fritchman, 1960b). Fritchman's (1960a) technique of removal of the t e e t h with a camel *s h a i r brush was f o l l o w e d . Specimens were s t a i n e d i n a c e t o -carmine or c h l o r a z o l b l a c k E, dehydrated completely, and mounted w i t h Permount u s i n g 22 mm square cover s l i p s . O b servations were made on s l i d e m a t e r i a l and on unmounted specimens. Camera l u c i d a diagrams were based on p r e p a r a -t i o n s f o r which mounting d i s t o r t i o n e f f e c t s were n e g l i g i b l e . The p a t t e r n of loops made by the r a d u l a r sheath . w i t h i n the v i s c e r a l mass ( r a d u l a r c o n f i g u r a t i o n ) was i n v e s t i g a t e d . Observations were made on s i x t y animals of each o f the three s p e c i e s . The sample c o n s i s t e d o f twenty animals of each s p e c i e s c o l l e c t e d from Bowen I s -l a n d , twenty from B a m f i e l d , and twenty from S t a n l e y Park. S i z e s ranged from one to f o u r cm i n s h e l l l e n g t h . The 21 specimens were h e l d f o r one week i n the l a b o r a t o r y , a n e s t h e t i z e d i n 7.5% MgCl^I^O ( i n tap water), and p r e -served i n 5% n e u t r a l f o r m a l i n f o r one more week. Photographs were made of each i n d i v i d u a l , f i r s t b e f o r e d i s s e c t i o n w i t h o n l y the s h e l l removed, and then a f t e r removal o f the v i s c e r a , l e a v i n g o n l y the r a d u l a r sheath w i t h i n the v i s c e r a l c a v i t y . D i s s e c t i n g p i n s were p l a c e d among the r a d u l a r loops i n order to prevent sagging o r u n f o l d i n g o f the s t r u c t u r e as the su p p o r t i n g v i s c e r a were removed. Photographs were taken w i t h a Nikon F2 camera and e x t e n s i o n tubes, and a Honeywell r i n g f l a s h . Photographic n e g a t i v e s were en l a r g e d so t h a t each animal measured 6 cm i n body l e n g t h on the p r i n t . T r a c i n g s were made of each p r i n t , and the t r a c i n g s were overlapped and composite drawings made of the r a d u l a r loops. Com-p o s i t e diagrams were made i n order t o demonstrate i n t r a -s p e c i f i c v a r i a t i o n . Measurements of t o t a l l e n g t h o f the r a d u l a were taken along w i t h wet weight o f s o f t p a r t s and s h e l l l e n g t h f o r 50 i n d i v i d u a l s o f each o f the three s p e c i e s . Animals were h e l d i n the l a b o r a t o r y f o r one week and then removed from t h e i r s h e l l s u s i n g a b l u n t s p a t u l a . S h e l l l e n g t h s were taken u s i n g v e r n i e r c a l i p e r s (+0.1 mm). The animals were damp-dried wi t h f i l t e r paper. Wet weights were taken on a M e t t l e r Balance (+0.1 mg). A f t e r weighing, the e n t i r e r a d u l a was d i s s e c t e d from each animal and s t r e t c h e d out on a large coverglass (60 mm x 48 mm). Two small coverglasses (60 mm X 24 mm) were placed on either side of the radula lengthwise to make i t completely l i n e a r . Another large coverglass was placed over the radula with a few drops of d i s t i l l e d water. Length measurements were taken on a L e i t z dissecting microscope (at 8X magnification) using an ocular micrometer (+ 0.1 mm). The measurement was taken from the posterior end of the radula to the anterior end at the point where the radular row became so transparent that i t could not be seen. The radular bulb was not included i n the length measurement. The length of each radula was taken three times and the average recorded. Regression analysis was performed on the two sets of data (radular length versus w e t w e i g h t , and radular length versus s h e l l length). S t a t i s t i c s for both the functional and predictive regressions were ob-tained, but since there was less than a 5% difference between the two regression l i n e s , only the predictive l i n e s and equations are given. An analysis of covariance was used to determine significance of the regression l i n e s . The l e v e l of significance was set at p = 0.01. Examination of the Jaw Light microscope preparations of the jaw were attempted using 1 mm rings for thick mounting, but d i f f i c u l t i e s were encountered i n the dehydration phases and substitution with xylene. These treatments tended to shrink the edges of the structure, s l i g h t l y d i s t o r t i n g the shape. Such d i s t o r t i o n s were not produced i n S.E.M. p r e p a r a t i o n s . The s t r u c t u r e was d i s s e c t e d i n t a c t from animals which had p r e v i o u s l y been f r o z e n and thawed. Th i s treatment separated the a t t a c h e d muscles from the jaw. The jaws were washed i n d i s t i l l e d water, t r a n s -f e r r e d to v i a l s c o n t a i n i n g 70% e t h a n o l , and p l a c e d i n an u l t r a s o n i c c l e a n e r f o r two to f i v e minutes. T h i s e f f e c -t i v e l y removed p i e c e s o f a t t a c h e d muscle and d e b r i s from the jaw s u r f a c e . The specimens were dehydrated and d r i e d by the c r i t i c a l p o i n t d r y i n g method. They were mounted on aluminum stubs u s i n g s i l v e r p a i n t , some wit h the v e n t r a l s u r f a c e upward and some with the d o r s a l s u r -face upward. Gold c o a t i n g was e s s e n t i a l , as uncoated jaws were found to be unstable under the e l e c t r o n beam. A t o t a l o f twenty jaws of each o f the three s p e c i e s were examined i n a Cambridge Mark 2A s t e r e o s c a n . Gross Morphology of the Gut F i v e animals o f each of the three s p e c i e s were d i s s e c t e d to r e v e a l the p a t t e r n of l o o p i n g o f the i n t e s -t i n e through the v i s c e r a l mass. Specimens were anes-t h e t i z e d i n 7.5% MgCl 26H 20 and p r e s e r v e d i n 5% n e u t r a l f o r m a l i n f o r approximately one week. The d i g e s t i v e gland, r a d u l a , and gonad were removed, l e a v i n g the eso-phagus, stomach, p r o v e n t r i c u l u s , and i n t e s t i n e i n t h e i r n a t u r a l p o s i t i o n s . D i s s e c t i o n s were photographed u s i n g a Nikon F2 camera and e x t e n s i o n tubes. Freehand drawings were made from the d i s s e c t i o n s . 24 The e x t e n t o f the s a l i v a r y gland i n each o f the three s p e c i e s was determined by d i s s e c t i o n of f o r m a l i n -p r e s e r v e d m a t e r i a l . Twenty to t h i r t y animals o f each s p e c i e s were examined. Because of the d i f f i c u l t y i n d i s -t i n g u i s h i n g t h i s s t r u c t u r e from the d i g e s t i v e gland, s e r i a l s e c t i o n s o f fou r t o f i v e animals o f each s p e c i e s were ex-amined to c o n f i r m o b s e r v a t i o n s made on d i s s e c t e d specimens. The morphology of d i g e s t i v e gland t u b u l e s was examined i n approximately f i f t y animals o f each s p e c i e s . Specimens were preserved i n 5% n e u t r a l f o r m a l i n f o r one to two weeks. A f t e r removal of the s h e l l and the d o r s a l mantle, the tu b u l e s and t h e i r arrangement were examined at the exposed s u r f a c e . D i s s e c t i o n of the gland was made i n order to observe tubul e morphology a t deeper l e v e l s . Freehand drawings were made from the d i s s e c t i o n s . An a l t e r n a t e method was attempted t o document the morphology of d i g e s t i v e gland t u b u l e s . I n j e c t i o n of the al i m e n t a r y t r a c t u s i n g a p l a s t i c i n j e c t i o n medium ( v i n y l acetate) was c a r r i e d out on a l l t h r e e s p e c i e s , but i n -j e c t i o n of the e n t i r e gland was achieved o n l y i n C. p e l t a . Each l i m p e t was a n e s t h e t i z e d • i n 7.5% MgC^BH^O f o r two to ten minutes. The plunger of a 10 cc g l a s s s y r i n g e was f i r s t l u b r i c a t e d w i t h v a s e l i n e to a l l o w smooth i n j e c t i o n and then f i l l e d w i t h v i n y l a c e t a t e and atta c h e d to a 20 gauge needle. The needle was i n s e r t e d i n t o the bu c c a l c a v i t y , and the neck t i e d around i t w i t h s u r g i c a l t h r e a d . Approximately 0.2 ml of p l a s t i c was i n j e c t e d 25 i n t o the animal. The canula was removed and the neck t i e d o f f to prevent escape o f the p l a s t i c . The animal was p l a c e d immediately i n t o tap water and l e f t one to two hours to al l o w the p l a s t i c to polymerize. The s o f t t i s s u e s were d i s s o l v e d i n conc e n t r a t e d NaOH and the r e -maining c a s t washed wi t h tap water. Since rupture i n t o o ther organs (such as the f o o t , gonad and mantle v e s s e l s ) u s u a l l y o c c u r r e d , the c a s t s were d i s s e c t e d to leave o n l y the i n j e c t e d p o r t i o n s o f the d i g e s t i v e t r a c t . Casts o f p o r t i o n s o f the d i g e s t i v e gland were ob-t a i n e d from specimens of C. p e l t a . Although numerous specimens of the other two s p e c i e s were i n j e c t e d , c a s t s of o n l y two or three t u b u l e s of the d i g e s t i v e gland were ob t a i n e d . In p r a c t i c a l l y every specimen of C. persona and C. scutum i n j e c t e d , l a r g e r u p t u r e s o c c u r r e d b e f o r e the p l a s t i c reached the duct of the d i g e s t i v e gland. Attempts made a t u s i n g a i r - r e g u l a t e d low i n j e c t i o n p r e s s u r e s i n -stead o f hand s y r i n g e i n j e c t i o n proved l e s s s u c c e s s f u l . The p l a s t i c c a s t s made of C_. p e l t a were photographed u s i n g a Nikon F2 camera wi t h e x t e n s i o n tubes. H i s t o l o g y and H i s t o c h e m i s t r y o f the gut and a s s o c i a t e d glands Animals to be used i n h i s t o l o g i c a l i n v e s t i g a t i o n s were a n e s t h e t i z e d i n 7.5% MgC^o^O, pre s e r v e d i n Bouin's f l u i d , dehydrated i n e t h a n o l and c l e a r e d i n methyl ben-zoate. A f t e r r i n s i n g i n xylene they were i n f i l t r a t e d f o r one and one h a l f to two hours i n an Autotechnicon U l t r a 26 T i s s u e P r o c e s s o r , and embedded i n p a r a f f i n . S e r i a l sec-t i o n s were made of e i g h t animals u s i n g a L e i t z Rotary (Minot 1212) microtome (three specimens of C. persona, three specimens of C. scutum, and two specimens of C. p e l t a ) . Some s e r i a l s were cu t a t 10 micrometers, and some were cut a t 5. In a d d i t i o n , twenty to t h i r t y s e c t i o n s each of s i x more animals were taken a t 0.5 mm i n t e r v a l s throughout the e n t i r e animal. S e c t i o n e d mate-r i a l was s t a i n e d w i t h Mayer's or D e l a f i e l d ' s haematoxylin and c o u n t e r s t a i n e d w i t h e o s i n . Three h i s t o c h e m i c a l methods were used to a i d i n the i d e n t i f i c a t i o n of mucocytes and o t h e r s e c r e t o r y c e l l s . Some s e c t i o n s were s t a i n e d by the P e r i o d i c a c i d - S c h i f f technique (P.A.S.) (Pearse, 1968). 2 , 4 - d i n i t r o p h e n y l -hydrazine (D.N.P.H.) was employed as an aldehyde block and a c e t y l a t i o n was used as the c o n t r o l method (Pearse, 1968). Mayer's haematoxylin was used as a c o u n t e r s t a i n . A l c i a n blue s t a i n i n g was c a r r i e d out a t pH 2.5, along w i t h m i l d m e t h y l a t i o n (at 37°C) and s a p o n i f i c a t i o n as c o n t r o l s (Pearse, 1968). These s e c t i o n s were c o u n t e r s t a i n e d w i t h e o s i n . T o l u i d i n e blue s t a i n i n g was employed a t pH 4.2 to t e s t f o r metachromasia (Chayen, et a l , 1 9 7 3 ) . A l l meta-chromasia found was of the beta type ( p u r p l e ) . Heidenhain's i r o n haematoxylin was used to demonstrate s e c r e t o r y c e l l s (Humason, 1962). C e l l h e i g h t and c i l i a l e n g t h from v a r i o u s r e g i o n s of the a l i m e n t a r y system were measured from s e c t i o n s of 27 seven animals u s i n g a Z e i s s microscope and o c u l a r micro-meter, a c c u r a t e t o 3 micrometers. The range of measure-ments r e p o r t e d i n c l u d e d the range over the seven animals examined. Photographs of s e c t i o n e d m a t e r i a l were taken w i t h a Z e i s s Photomicroscope I I . Panatomic X f i l m was used, w i t h green and blue f i l t e r s . Examination o f F e c a l P e l l e t s Approximately 100 animals of each s p e c i e s were c o l l e c t e d and h e l d i n three separate tanks o v e r n i g h t . The p e l l e t s , w h i c h had been shed d u r i n g t h i s p e r i o d were examined w i t h a d i s s e c t i n g microscope, and photographed u s i n g a Nikon F2 camera and e x t e n s i o n tubes. Measure-ments o f p e l l e t dimensions were taken on a L e i t z b i n o c u l a r microscope u s i n g an o c u l a r micrometer (+ 0.1 mm). 28 I I I . RESULTS A. Morphology of the Radula 1. The Radular Teeth The radula i n the Acmaeidae i s of the doco-glossate type. General c h a r a c t e r i s t i c s of t h i s r a -dula type are discussed i n d e t a i l i n Fretter and Graham (1962) and Hyman (1967). B r i e f l y , there are one or two pairs of l a t e r a l teeth per row, usually with strongly pigmented t i p s . The genus C o l l i s e l l a i s characterized by a single pair of inner l a t e r a l s i n one row, and posterior to these are a pair of median l a t e r a l s which are flanked by a pair of . smaller outer l a t e r a l s . The central (= rachidian) tooth i s absent. The subgenus C o l l i s e l l a (includes C. pelta) i s characterized by a pair of rudimentary marginal teeth, c a l l e d uncini, located on the ribbon margin (McLean, 1966). In the subgenus Notoacmaea (includes C. scutum and C. persona) uncini are ab-sent. Thus, the formulae for the radular teeth i n the three species are: C. pelta r l + 3 + 0 + 3 + l r C. scutum 0 + 3 + 0 + 3 + 0 C. persona 0 + 3 + 0 + 3 + 0 r rudimentary 29 As p o i n t e d out by Hyman (1967), there are d i s c r e p a n -c i e s i n r a d u l a r terminology. For purposes o f c l a r i t y , t h e r e -f o r e , terms w i l l be d e f i n e d as f o l l o w s : 1. Base - the f l a t p o r t i o n of the r a d u l a r t o o t h which i s p a r a l l e l to the r a d u l a r r i b b o n . I t i s the p a r t by which the t o o t h i s att a c h e d to the b a s a l p l a t e s . 2. Cusp - the r a i s e d p o r t i o n o f the t o o t h which i s approximately p e r p e n d i c u l a r t o the rib b o n a x i s . 3. Segment - each u n i t o f the r i b b o n which i s made up o f a p a i r o f i n n e r , median, and outer l a t e r a l t e e t h . 4. B a s a l P l a t e s - the c h i t i n o u s p l a t e s beneath each r a d u l a r t o o t h . In F i g u r e 4 a r a d u l a r segment of C. p e l t a i s d i a -grammed, and important f e a t u r e s are i n d i c a t e d . The r a d u l a r t e e t h o f C. p e l t a , C. persona, and C. scutum d i f f e r i n two ways: 1. In the form o f the t e e t h 2. In the s p a t i a l r e l a t i o n s h i p s o f the t e e t h . I n t r a s p e c i f i c v a r i a t i o n i s n e g l i g i b l e . T h i s was a l s o found by C u r t i s s (1941) and McLean (1966). I t i s r e c o g n i z e d t h a t one of the major problems i n the documentation o f r a d u l a r t e e t h i s the use o f s u b j e c t i v e terminology. Though the use of such terms cannot be avoided e n t i r e l y , an e f f o r t has been made i n the pr e s e n t paper to 30 F i g u r e 4. Diagram o f a r a d u l a r segment of C o l l i s e l l a p e l t a showing the important f e a t u r e s o f the l a t e r a l t e e t h . M a g n i f i c a t i o n approximately 200X. A, a n t e r i o r ; CA, concave a r c ; CF, concave face on o u t e r l a t e r a l ; DT, d o r s a l t i p o f o u t e r l a t e r a l ; IL, i n n e r l a t e r a l t o o t h ; ML, median l a t e r a l t o o t h ; OL, o u t e r l a t e r a l t o o t h ; P, p o s t e r i o r ; RM, r i b b o n margin; U, uncinus; VT, v e n t r a l t i p of o u t e r l a t e r a l . 32 minimize d e s c r i p t i v e terminology. F u r t h e r , the d i s c u s s i o n w i l l be l i m i t e d to o n l y those f e a t u r e s which serve t o d i s -t i n g u i s h the r a d u l a e . The c h a r a c t e r s which were found to d i s t i n g u i s h the r a d u l a r t e e t h are the f o l l o w i n g : A. The Inner L a t e r a l s (Table la) 1. degree of a n t e r i o r c u r v a t u r e along the cusp 2. sharpness of the t i p s 3. degree of a n t e r o - p o s t e r i o r and/or l a t e r a l i n c l i n a t i o n o f the cusp 4. c o n c a v i t y and c o n v e x i t y of the a n t e r i o r and p o s t e r i o r faces of the cusps 5. h e i g h t of i n n e r and median l a t e r a l s ( r e -l a t i v e to each other) 6. presence or absence of s c u l p t u r i n g on the p o s t e r i o r face of the cusp B. The Median L a t e r a l s (Table lb) 1. degree of a n t e r i o r c u r v a t u r e a l o n g the cusp 2. sharpness of the t i p s 3. degree of a n t e r o - p o s t e r i o r and/or l a t e r a l i n c l i n a t i o n of the cusp 4. c o n c a v i t y and c o n v e x i t y o f the a n t e r i o r and p o s t e r i o r faces of the cusps 6. presence or absence of s c u l p t u r i n g on the p o s t e r i o r face of the cusp 7. presence or absence of o v e r l a p of the cusp to the adjacent segment 33 8. prominence of the t e r m i n a l hook 9. presence or absence of a concave arc on the p o s t e r i o r face of the cusp. C. The Outer L a t e r a l s (Table l c ) 2. sharpness of the t i p s 3. degree o f a n t e r o - p o s t e r i o r and/or l a t e r a l i n c l i n a t i o n of the cusp 10. r e l a t i v e s i z e o f the o u t e r l a t e r a l s 11. r e l a t i v e p o s i t i o n s of the d o r s a l and ven-t r a l t i p s of the o u t e r l a t e r a l s 12. shape of the a n t e r i o r f a c e of the o u t e r l a t e r a l s D. U n c i n i (Table Id) 13. presence or absence of u n c i n i A complete l i s t o f d i s t i n g u i s h i n g c h a r a c t e r s o f each of the l a t e r a l t e e t h f o r f o u r s p e c i e s (C. p e l t a , C. scutum, C. persona, and C. l i m a t u l a ) i s given i n Tables l a , l b , and l c . In p r a c t i c e , however, i t was found t h a t the radulae of these C o l l i s e l l a s p e c i e s c o u l d be d i s t i n g u i s h e d by u s i n g f o u r of the above l i s t e d f e a t u r e s (1, 2, 3, and 13). These f e a -t u r e s are d i s c u s s e d below f o r each s p e c i e s . In C o l l i s e l l a p e l t a there i s a very g r e a t a n t e r i o r c u r v a t u r e o f the median l a t e r a l s ( F i g s . 5a t o 5d). The t i p s . of a l l l a t e r a l t e e t h are s h a r p l y p o i n t e d . U n c i n i are pre-sent along the r i b b o n margin. The rock d w e l l i n g form and the E g r e g i a form o f t h i s s p e c i e s have i d e n t i c a l r a d u l a r teeth. 34 In C o l l i s e l l a scutum, while the cusps of the median l a t e r a l s are i n c l i n e d a n t e r i o r l y , there i s very l i t t l e c u r -v a t u r e along the l e n g t h ( F i g s . 6a t o 6d). The t i p s o f a l l l a t e r a l t e e t h are b l u n t , and u n c i n i are l a c k i n g . The median l a t e r a l s o f C o l l i s e l l a persona stand s t r a i g h t and e r e c t . There i s no a n t e r i o r c u r v a t u r e along the cusp and almost no a n t e r i o r i n c l i n a t i o n ( F i g s . 7a t o 7d). The t i p s o f a l l l a t e r a l t e e t h have rounded and b l u n t t i p s . U n c i n i are absent. In C o l l i s e l l a l i m a t u l a the median l a t e r a l s are i n c l i n e d a n t e r i o r l y , but there i s no c u r v a t u r e along the cusp ( F i g s . 8a to 8d). A l l l a t e r a l t e e t h are b l u n t and rounded a t the t i p s . U n c i n i are p r e s e n t along the r i b b o n margin. 35 Table 1: Summary o f the Morphology o f the Radular Teeth A. Inner L a t e r a l s C h a r a c t e r number C. p e l t a C. scutum * C. persona C. l i m a t u l a 1 moderate a n t e r i o r c u r v a t u r e moderate a n t e r i o r c u r v a t u r e very s l i g h t a n t e r i o r c u r v a t u r e very s l i g h t a n t e r i o r c u r v a t u r e 2 t i p s sharp-l y p o i n t e d t i p s b l u n t t i p s b l u n t and very rounded t i p s b l u n t and very rounded 3 stand n e a r l y e r e c t s l i g h t p o s t e r i o r and l a t e r a l i n c l i n a t i o n , s l i g h t p o s t e r i o r and l a t e r a l i n c l i n a t i o n v e ry s l i g h t p o s t e r i o r i n c l i n a t i o n ; pronounced l a t e r a l i n c l i n a t i o n 4 a n t e r i o r f a c e concave a n t e r i o r face concave a n t e r i o r face f l a t a n t e r i o r f ace almost f l a t 5 cusps s h o r t e r than those o f median l a t e r a l s cusps l o n g e r than those o f median l a t e r a l s cusps l o n g e r than those of median l a t e r a l s cusps l o n g e r than those o f median l a t e r a l s 6 no s c u l p -t u r i n g on p o s t e r i o r f a c e r i d g i n g on p o s t e r i o r face r i d g i n g on p o s t e r i o r face no s c u l p -t u r i n g on p o s t e r i o r face 36 Table 1: Summary of the Morphology o f the Radular Teeth B. Median L a t e r a l s C h a r a c t e r number C. p e l t a C. scutum C. persona C. l i m a t u l a 1 cusps wi t h g r e a t ant-e r i o r c u r v a t u r e cusps i n -c l i n e d a n t e r i o r l y but with l i t t l e c u r v a t u r e very s l i g h t a n t e r i o r i n c l i n a t i o n ; no c u r v a t u r e of cusp cusps i n -c l i n e d ante-r i o r l y but w i t h no c u r v a t u r e 2 t i p s sharp-l y p o i n t e d t i p s b l u n t t i p s b l u n t and very rounded t i p s b l u n t and v e r y rounded 3 cusps d i r -e c t e d a n t -e r o - l a t -e r a l l y cusps d i r -e c t e d ant-e r i o r l y cusps d i r -e c t e d s l i g h t l y a n t e r i o r l y cusps d i r -e c t e d ant-e r o - l a t -e r a l l y 4 a n t e r i o r face concave a n t e r i o r face s l i g h t -l y concave a n t e r i o r face f l a t a n t e r i o r face f l a t 6 no s c u l p -t u r i n g on p o s t e r i o r face no s c u l p -t u r i n g on p o s t e r i o r face r i d g i n g on p o s t e r i o r face no s c u l p -t u r i n g on p o s t e r i o r f a c e 7 o v e r l a p i n n e r l a t -e r a l s o f a d j a c e n t segment reach but do not o v e r l a p i n n e r l a t -e r a l s of a d j a c e n t segment do not reach i n n e r l a t e r a l s o f a d j a c e n t segment o v e r l a p i n n e r l a t -e r a l s o f a d j a c e n t segment 8 prominent t e r m i n a l hook very s l i g h t t e r m i n a l hook no t e r m i n a l hook no t e r m i n a l hook 9 concave a r c on p o s t e r i o r f a c e no a r c no a r c no a r c 37 Table 1: Summary o f the Morphology of the Radular Teeth C. Outer L a t e r a l s C h a r a c t e r number C. p e l t a C. scutum C. persona C. l i m a t u l a 2 t i p s sharp-l y p o i n t e d t i p s rounded t i p s v e r y rounded t i p s v ery rounded 3 t i p s d i r -e c t e d ant-e r i o r l y d o r s a l t i p d i r -e c t e d l a t -e r a l l y ; v e n t r a l t i p a nt-e r o - l a t -e r a l l y t i p s d i r -e c t e d ant-e r i o r l y and very s l i g h t -l y l a t e r a l l y d o r s a l t i p d i r e c t e d l a t e r a l l y ; v e n t r a l t i p a n t e r o -l a t e r a l ^ 10 l a r g e s m a l l e r than i n C. p e l t a s m a l l s m a l l e r than i n C. p e l t a 11 v e n t r a l t i p almost d i r e c t l y beneath d o r s a l t i p d o r s a l t i p s l i g h t l y p o s t e r i o r to v e n t r a l t i p d o r s a l t i p s l i g h t l y p o s t e r i o r to v e n t r a l t i p v e n t r a l t i p almost d i r e c t l y beneath d o r s a l t i p 12 a n t e r i o r edge con-cave a n t e r i o r edge s t r a i g h t a n t e r i o r edge s l i g h t -l y concave a n t e r i o r edge s l i g h t l y concave D. O n c i n i C h a r a c t e r number C. p e l t a C. scutum C. persona C. l i m a t u l a 13 s m a l l and s t r a i g h t ; b l u n t t i p ; a n t e r i o r l y d i r e c t e d absent absent s m a l l and s l i g h t l y S-shaped; b l u n t t i p a n t e r i o r l y d i r e c t e d 38 F i g u r e 5. Scanning e l e c t r o n micrographs showing d i f f e r e n t views o f the r a d u l a of C o l l i s e l l a p e l t a ; (a) viewed a t an angle from the a n t e r i o r , (b) viewed from the l e f t s i d e , (c) viewed from the a n t e r i o r , (d) viewed from the p o s t e r i o r . M a g n i f i c a t i o n a pproximately 100X. A, a n t e r i o r ; I L , i n n e r l a t e r a l t o o t h ; ML, median l a t e r a l t o o t h ; OL, o u t e r l a t e r a l t o o t h ; P, p o s t e r i o r 40 F i g u r e 6. Scanning e l e c t r o n micrographs showing d i f f e r e n t views of the r a d u l a o f C o l l i s e l l a scutum; (a) viewed a t an angle from the a n t e r i o r , (b) viewed from the l e f t s i d e , (c) viewed from the a n t e r i o r , (d) viewed from the p o s t e r i o r . M a g n i f i c a t i o n approximately 100X. A, a n t e r i o r ; IL, i n n e r l a t e r a l t o o t h ; ML, median l a t e r a l t o oth; OL, o u t e r l a t e r a l t o o t h ; P, p o s t e r i o r . 42 F i g u r e 7. Scanning e l e c t r o n micrographs showing d i f f e r e n t views of the r a d u l a of C o l l i s e l l a persona; (a) viewed a t an angle from the a n t e r i o r , (b) viewed from the l e f t s i d e , (c) viewed from the a n t e r i o r , (d) viewed from the p o s t e r i o r . M a g n i f i c a t i o n approximately 100X. A, a n t e r i o r ; IL, i n n e r l a t e r a l t o o t h ; ML, median l a t e r a l t o oth; OL, o u t e r l a t e r a l t o o t h ; P, p o s t e r i o r . 44 F i g u r e 8. Scanning e l e c t r o n micrographs showing d i f f e r e n t views of the r a d u l a of C o l l i s e l l a l i m a t u l a ; (a) viewed a t an angle from the a n t e r i o r , (b) viewed from the l e f t s i d e , (c) viewed from the a n t e r i o r , (d) viewed from the p o s t e r i o r . M a g n i f i c a t i o n approximately 100X. A, a n t e r i o r ; IL, i n n e r l a t e r a l t o o t h ; ML, median l a t e r a l t o oth; OL, outer l a t e r a l t o o t h ; P, p o s t e r i o r . 46 2. B a s a l P l a t e s o f the Radula The p l a t e s are arranged i n b i l a t e r a l l y symme-t r i c a l p a i r s , each p a i r forming a row. The rows run along almost the e n t i r e l e n g t h of the r a d u l a r r i b b o n , f a d i n g near the p o s t e r i o r end where s e c r e t i o n o f the te e t h and p l a t e s takes p l a c e . Each member o f a p a i r i s i n t u r n composed o f two p l a t e s , one o v e r l y i n g the oth e r . These are the d o r s a l p l a t e and the v e n t r a l p l a t e . The s o - c a l l e d c e n t r a l (=anterior) and l a t e r a l (=posterior) t o o t h p l a t e s o f Fritchman (1960b; i n I l l g , 1969) were not found. Rather, a s i n g l e d o r s a l and a s i n g l e v e n t r a l p l a t e were observed i n each of the s p e c i e s s t u d i e d . The d o r s a l p l a t e o v e r l a p s the v e n t r a l f o r much of i t s area, but i n a l l three s p e c i e s the a n t e r i o r margin o f the d o r s a l p l a t e extends pa s t t h a t o f the v e n t r a l p l a t e . The v e n t r a l p l a t e s t a i n s d a r k l y i n a l l t h ree s p e c i e s (with acetocarmine and c h l o r a z o l b l a c k E ) . The d o r s a l p l a t e s t a i n s f a i n t l y , and i n mounted specimens i t i s very d i f f i c u l t to determine the p o s i t i o n o f the margins, e s p e c i a l l y where they o v e r l a p the v e n t r a l p l a t e . The shapes of the d o r s a l and v e n t r a l b a s a l p l a t e s are d i s t i n c t f o r each s p e c i e s . V a r i a t i o n i n the shapes of mounted p l a t e s i s due l a r g e l y to squashing e f f e c t s o f the c o v e r s l i p , as determined by examina-t i o n o f unmounted ra d u l a e . I n d i v i d u a l v a r i a t i o n 47 w i t h i n a s p e c i e s was found to be s l i g h t , i n no way approaching o v e r l a p between s p e c i e s . In F i g u r e 9 the b a s a l p l a t e s o f C. p e l t a are shown wit h the important comparative f e a t u r e s l a b e l l e d . Shapes o f i n d i v i d u a l p l a t e s of a l l three s p e c i e s are shown i n F i g u r e 12. The c h a r a c t e r s which were found to d i s t i n g u i s h the b a s a l p l a t e s are the f o l l o w i n g : A. The V e n t r a l P l a t e 1. r e l a t i v e width of the a n t e r i o r lobe and sharpness of the t i p 2. p r o x i m i t y of medial margins 3. angle formed by the l a t e r a l and p o s t e r i o r margins 4. shape of the p o s t e r i o r margin 5. . r e l a t i v e l e n g t h versus width o f p l a t e B. The D o r s a l P l a t e 6. p r o x i m i t y of a n t e r i o r margin to the adjacent segment 7. p r o x i m i t y o f medial margins and s i z e of median divergence 8. angle of p o s t e r i o r margin with r e s p e c t to the r i b b o n edge C. Median P l a t e l e t 9. presence or absence of median p l a t e l e t D. O u t l i n e of both p l a t e s 10. shape of the o u t l i n e of both the d o r s a l 48 and the ventral plate E. Spacing of ribbon units 11. spacing of medial and antero-posterior margins along the ribbon. A complete l i s t of the distinguishing characters of each of the three species i s given i n Table 2. In practice, however, i t was found that the basal plates of these C o l l i s e l l a species could be distinguished by using four of the above l i s t e d features (1, 4, 10, and 11). These features are discussed below for each species. In C. pelta the anterior lobe of the ventral plate i s wide and blunt at the t i p (Fig. 9). The post-e r i o r margin of the ventral plate i s straight and situated perpendicular to the ribbon axis. There i s a marked i n f l e x i o n near the l a t e r a l margin (Fig. 9, PI). The outline of both the dorsal and ventral plates forms an almost perfect rectangle, being longest i n the antero-posterior axis (Fig. 9, OutDVP). The ribbon units are c l o s e l y linked. The dorsal plate overlaps the posterior margin of the adjacent segment and the anterior and posterior medial margins meet. The anterior lobe of C. scutum i s narrow and the t i p s are pointed (Fig. 10). The posterior margin of the ventral plate i s s l i g h t l y convex and i s s l i g h t l y oblique with respect to the ribbon margin. The outline of the dorsal and ventral plates together present an 49 almost parallelogram shape (Fig. 10, OutDVP). Length approximately equals width. The ribbon units are well spaced. There i s no dorsal plate overlap, but the the t i p s of the anterior lobes contact the posterior margins of adjacent segments. Medial margins are close but do not meet. In C. persona the anterior lobe i s narrow and the tips.are sharply pointed and curved toward the midline (Fig. 11). The posterior margin of the ventral plate has a pronounced V-shape, the apex of the V situated closer to the l a t e r a l margin. The outline of the dorsal and ventral plates presents a d i s t i n c t concavo-convex shape, with a strongly concave anterior margin and a strongly convex posterior margin (Fig. 11, OutDVP). Length almost equals width. Ribbon units are well spaced. There i s no antero-posterior contact of units. Medial margins meet or are close. In general, the present results concur with those reported by Grant (1937). The diagrams of both Grant (1937) and Fritchman (in I l l g , 1969), however, show the dorsal and ventral plates as proportionately greater i n length than was found for C. scutum. Grant (1937) and Curtiss (1941) report that the "segments" of both C. pelta and C. scutum are a l i t t l e broader than long. This description i s considered to be misleading, since a segment width includes the width across two plates, whereas the length i s measured along 50 one p l a t e o n l y . I f a s i n g l e p l a t e ( d o r s a l o r v e n t r a l ) i s c o n s i d e r e d , then i n C. p e l t a the l e n g t h i s always g r e a t e r than the width, and i n C. scutum the l e n g t h very n e a r l y equals the width. T h i s f e a t u r e serves to d i s t i n g u i s h very c l e a r l y the p l a t e s o f these two s p e c i e s . 51 F i g u r e 9. Diagram of s e v e r a l r a d u l a r segments of C o l l i s e l l a p e l t a showing the b a s a l p l a t e s . The v e n t r a l p l a t e s are shaded. The segment at the top of the page shows the out-l i n e of the o v e r l a p p i n g d o r s a l and v e n t r a l p l a t e s . At the bottom of the page a p a i r of d o r s a l p l a t e s i s shown wit h the p o s i t i o n of the l a t e r a l t e e t h i n d i c a t e d with dashed l i n e s . M a g n i f i c a t i o n approximately 100X. A, a n t e r i o r ; AL, a n t e r i o r lobe; AM, a n t e r i o r margin; DP, d o r s e l p l a t e ; LM, l a t e r a l margin; MD, median divergence; MM, medial margin; MP, median p l a t e l e t ; OutDVP, o u t l i n e of the d o r s a l and v e n t r a l p l a t e s ; P, p o s t e r i o r ; PI, p o s t e r i o r i n f l e x i o n ; PIL, p o s i t i o n of i n n e r l a t e r a l t o o t h ; PM, p o s t e r i o r margin; PML, p o s i t i o n of median l a t e r a l t o o t h ; POL, p o s i t i o n of outer l a t e -r a l t o o t h ; RM, r i b b o n margin; U, uncinus; VP, v e n t r a l p l a t e . 52 53 F i g u r e 10. Diagram of s e v e r a l r a d u l a r segments of C o l l i s e l l a scutum showing the b a s a l p l a t e s . The v e n t r a l plates are shaded. The segment a t the top of the page shows the o u t l i n e of the o v e r l a p p i n g d o r s a l and v e n t r a l p l a t e s . At the bottom o f the page a p a i r o f d o r s a l p l a t e s i s shown w i t h the p o s i t i o n of the l a t e r a l t e e t h i n d i c a t e d with d o t t e d l i n e s . M a g n i f i c a -t i o n approximately 10OX. A, a n t e r i o r ; AL, a n t e r i o r lobe; DP, d o r s a l p l a t e ; OutDVP, out-l i n e o f the d o r s a l and v e n t r a l p l a t e s ; P, p o s t e r i o r ; PIL, p o s i t i o n o f i n n e r l a t e r a l t o o t h ; PML, p o s i t i o n o f median l a t e -r a l t ooth; POL, p o s i t i o n o f outer l a t e r a l t ooth; RM, r i b b o n margin; VP, v e n t r a l p l a t e . 54 55 F i g u r e 11. Diagram of s e v e r a l r a d u l a r segments of C o l l i s e l l a persona showing the b a s a l p l a t e s . The v e n t r a l p l a t e s are shaded. The segment a t the top of the page shows the o u t l i n e o f the o v e r l a p p i n g d o r s a l and v e n t r a l p l a t e s . A t the bottom of the page a p a i r o f d o r s a l p l a t e s i s shown with the p o s i t i o n o f the l a t e r a l t e e t h i n d i c a t e d w i t h d o t t e d l i n e s . M a g n i f i c a t i o n approximately 100X. A, a n t e r i o r ; DP, d o r s a l p l a t e ; OutDVP, o u t l i n e o f the d o r s a l and v e n t r a l p l a t e s ; P, p o s t e r i o r ; PIL, p o s i t i o n o f i n n e r l a t e r a l t o o t h ; PML, p o s i t i o n o f median l a t e r a l t o o t h ; POL, p o s i t i o n o f ou t e r l a t e r a l t o o t h ; RM, r i b b o n margin; VP, v e n t r a l p l a t e . A P 57 F i g u r e 12. Diagram of r a d u l a r b a s a l p l a t e s showing the o u t l i n e s o f the l e f t d o r s a l and v e n t r a l p l a t e s t o g e t h e r (column i ) , and the o u t l i n e of each i n d i v i d u a l p l a t e , d o r s a l (column i i ) , and v e n t r a l (column i i i ) ; (a) C o l l i s e l l a scutum, (b) C o l l i s e l l a persona, (c) C o l l i s e l l a p e l t a . The f i g u r e s are composites o f approximately ten i n d i v i d u a l s o f each s p e c i e s . M a g n i f i c a t i o n approximately 100X. LDP, l e f t d o r s a l p l a t e ; L DVP, l e f t d o r s a l and v e n t r a l p l a t e s ; LVP, l e f t v e n t r a l p l a t e . 59 T a b l e 2: Summary o f t h e M o r p h o l o g y o f t h e B a s a l P l a t e s o f t h e R a d u l a P l a t e C h a r -a c t e r number C . p e l t a C . s c u t u m C . p e r s o n a 1 a n t e r i o r l o b e w i d e ; b l u n t a t t i p a n t e r i o r l o b e n a r r o w ; t i p s p o i n t e d a n t e r i o r l o b e n a r r o w ; t i p s v e r y p o i n t e d a n d c u r v e d t o w a r d m i d l i n e 2 p o s t e r i o r m e d -i a l m a r g i n s m e e t p o s t e r i o r m e d -i a l m a r g i n s c l o s e b u t d o n o t m e e t p o s t e r i o r m e d -i a l m a r g i n s n o t c l o s e V e n -t r a l P l a t e 3 l a t e r a l a n d p o s t e r i o r m a r -g i n s a t a p p r o x -i m a t e r i g h t a n g l e s t o e a c h o t h e r a n g l e f o r m e d b y l a t e r a l a n d p o s t e r i o r m a r g i n s l e s s t h a n 9 0 ° a n g l e f o r m e d b y l a t e r a l a n d p o s t e r i o r m a r g i n s g r e a t -e r t h a n 9 0 ° 4 p o s t e r i o r m a r -g i n s t r a i g h t w i t h m a r k e d l a t e r a l i n f l e -x i o n p o s t e r i o r m a r -g i n s l i g h t l y c o n c a v e w i t h a v e r y s l i g h t l a t e r a l i n -f l e x i o n p o s t e r i o r m a r g i n V -s h a p e d 5 p l a t e l o n g e r t h a n b r o a d p l a t e a s l o n g a s b r o a d a l m o s t a s b r o a d a s l o n g - 6 a n t e r i o r m a r -g i n s o v e r l a p a d j a c e n t s e g -m e n t a n t e r i o r m a r -g i n s do n o t t o u c h a d j a c e n t s e g m e n t a n t e r i o r m a r -g i n s do n o t t o u c h a d j a c e n t s e g m e n t D o r s a l P l a t e 7 a n t e r i o r a n d p o s t e r i o r m e d i a l m a r g i n s m e e t ; m e d i a n d i v e r g e n c e m a r k e d m e d i a l m a r g i n s c l o s e b u t d o n o t m e e t ; m e d -i a n d i v e r g e n c e s l i g h t a n t e r i o r a n d p o s t e r i o r m e d i a l m a r g i n s m e e t o r a r e c l o s e ; m e d i a n d i v e r g e n c e m a r k e d 8 p o s t e r i o r m a r -g i n p e r p e n d i c -u l a r t o r i b b o n e d g e p o s t e r i o r m a r -g i n a t s l i g h t a n g l e t o p e r -p e n d i c u l a r a x i s o f r i b b o n p o s t e r i o r m a r -g i n v e r y a n g l e d w i t h r e s p e c t t o a x i s o f r i b b o n 60 Table 2: Summary o f the Morphology o f the B a s a l P l a t e s o f the Radula (Continued) Charac- Ch a r a c t e r C. p e l t a C. scutum C. persona t e r number Median pres e n t ; absent absent p l a t e l e t 9 ve r y small almost per- almost a n t e r i o r mar-f e c t l y r e c - p a r a l l e l - g i n s t r o n g l y O u t l i n e 10 t a n g u l a r ; ogram concave; pos-o f both l e n g t h g r e a t - shaped; t e r i o r mar-p l a t e s e r than l e n g t h g i n s t r o n g l y width approx- convex; l e n -i m a t e l y gth almost equals equals width width r i b b o n r i b b o n r i b b o n u n i t s u n i t s u n i t s w e l l spaced, c l o s e l y w e l l no a n t e r o -Spacing o f 11 l i n k e d , spaced; no p o s t e r i o r r i b b o n both med- medial o r c o n t a c t be-u n i t s i a l l y and an t e r o - tween u n i t s ; a n t e r o - p o s t e r i o r t i p s o f ant -p o s t e r i o r - c o n t a c t e r i o r lobes i y between do not con-u n i t s but t a c t preced-t i p s of i n g segment; a n t e r i o r medial mar-lobes con- g i n s c o n t a c t t a c t p r e - or are c l o s e c e d i n g seg-ment 61 3. Mechanical Wear of the Radula In C o l l i s e l l a p e l ta , C. persona, and C. scutum there i s a c h a r a c t e r i s t i c pattern of wear which i s sim i l a r i n a l l three species (Figs. 13 to 15). Wear i s evident i n the f i r s t fourteen rows of radular teeth within the buccal cavity. Those teeth posterior to the f i r s t fourteen rows show no signs of wear. Damage i s severest i n the teeth at the most anterior end of the buccal cavity, the degree of wear gradually be-coming less i n the teeth towards the posterior end. The r e s u l t i s that the teeth at the anterior end of the cavity are worn down much more than those at the posterior end, so that there i s a gradual decrease i n the height of the l a t e r a l teeth from the posterior to the anterior. In the most anterior regions of wear the teeth are so abraded that almost the entire cusp of each l a t e r a l tooth i s worn down, leaving only the basal portion and a small raised hump marking the remnant of the tooth cusp (Figs. 13b, 14b, and 15b). Wear i n the teeth i s f i r s t seen as abrasion of the ti p s of the cusps. The t a l l e s t l a t e r a l teeth of each species are the f i r s t to show abrasion at the t i p s . In C. persona and C. scutum i t i s the inner l a t e r a l s which demonstrate the f i r s t signs of wear, those teeth being t a l l e r than the median or outer l a t e r a l s . In C. pelta i t i s the median l a t e r a l s which f i r s t become abraded. In a l l three species the 62 t e e t h are worn down r a p i d l y so t h a t a l l three l a t e r a l s evidence wear by the t h i r t e e n t h row. A l l the l a t e r a l t e e t h are worn down at approximately the same r a t e . As i n P a t e l l a v u l g a t a (Runham and Thornton, 19 67), the cusps are worn down a t a f a i r l y c o nstant angle. The worn cusps have a c h i s e l shape w i t h the abraded s u r f a c e a t approximately 40 to 50 degrees to the r a d u l a r r i b b o n ( F i g s . 13b, 14b, and 15b). U n l i k e t h a t of P a t e l l a , however, the abraded s u r f a c e i s s l i g h t l y concave ( r a t h e r than f l a t ) , w i t h s l i g h t rounding a t the edges, the c e n t r e o f the t o o t h being a l i t t l e more worn than the o u t e r edges ( F i g . 15b). In C. p e l t a , where the median l a t e r a l s are ex-tremely recurved, wear f i r s t appears not on the t i p s of the cusps, but on t h e i r a n t e r i o r convex s u r f a c e s . The whole of the recurved t i p , however, very r a p i d l y becomes worn away, and then a b r a s i o n proceeds as i n the median l a t e r a l s o f the other two s p e c i e s (a gradual wearing down o f the t i p s a t a 40 to 50 degree a n g l e ) . The extremely worn t e e t h (at the a n t e r i o r end o f the b u c c a l c a v i t y ) are c h a r a c t e r i z e d i n a l l three s p e c i e s by the presence of deep l o n g i t u d i n a l s p l i t s o r cracks on the a n t e r i o r s u r f a c e s of the cusps ( F i g s . 13b, 14b, and 15b). These occur i n both the i n n e r and median l a t e r a l s i n the f i r s t three to seven t o o t h rows. 63 F i g u r e 13. Scanning e l e c t r o n micrographs showing two d i f f e r e n t views o f both worn and unworn p o r t i o n s o f the r a d u l a of C o l l i s e l l a p e l t a ; (a) unworn t e e t h viewed from the l e f t s i d e , (b) worn t e e t h viewed from the l e f t s i d e , (c) unworn t e e t h viewed from the a n t e r i o r , (d) worn t e e t h viewed from the a n t e r i o r . M a g n i f i c a t i o n approximately 100X. A, a n t e r i o r ; P, p o s t e r i o r . 64 65 F i g u r e 14. Scanning e l e c t r o n micrographs showing two d i f f e r e n t views of both worn and unworn p o r t i o n s o f the r a d u l a o f C o l l i s e l l a scutum; (a) unworn t e e t h viewed from the l e f t s i d e , (b) worn t e e t h viewed from the l e f t s i d e , (c) unworn t e e t h viewed from the a n t e r i o r , (d) worn t e e t h viewed from the a n t e r i o r . M a g n i f i c a t i o n approximately 100X. A, a n t e r i o r ; P, p o s t e r i o r . 66 67 F i g u r e 15. Scanning e l e c t r o n micrographs showing two d i f f e r e n t views o f both worn and unworn p o r t i o n s o f the r a d u l a o f C o l l i s e l l a persona; (a) unworn t e e t h viewed from the l e f t s i d e , (b) worn t e e t h viewed from the l e f t s i d e , (c) un-worn t e e t h viewed from the a n t e r i o r , <d) worn t e e t h viewed from the a n t e r i o r . M a g n i f i c a t i o n ' approximately 100X. A, a n t e r i o r ; P, p o s t e r i o r . 68 69 4. C o n f i g u r a t i o n of the Radula The p a t t e r n of loops made by the r a d u l a as i t winds through the v i s c e r a l mass, c a l l e d the c o n f i g u r a -t i o n of the r a d u l a , i s d i s t i n c t i n the three s p e c i e s examined. a. C o l l i s e l l a persona In t h i s s p e c i e s r a d u l a r l e n g t h ( r e l a t i v e to body s i z e ) i s g r e a t e s t and the c o n f i g u r a t i o n i s the most complex. The r a d u l a r sheath passes poste-r i o r l y from the b u c c a l c a v i t y over the s u r f a c e of the odontophore, s i t u a t e d w i t h i n a m i d - d o r s a l groove. P o s t e r i o r to the b u c c a l mass the r a d u l a moves ven-t r a l l y , coming to l i e upon the pedal musculature. A t t h i s p o i n t the s t r u c t u r e e n t e r s the v i s c e r a l c a v i t y and makes two complete loops b e f o r e t e r -minating i n the r a d u l a r b u l b . The f i r s t o f these loops ( F i g . 16a, LP 1) i s d o r s a l i n p o s i t i o n and some or a l l of i t can u s u a l l y be seen through the mantle i n u n d i s s e c t e d animals ( F i g . 16b, LP 1). The loop i s long and the s i d e s are pressed together f o r much of t h e i r l e n g t h . T h i s s u p e r f i c i a l loop i s p o s t e r i o r i n p o s i t i o n , making an arc which passes from the r i g h t m i d - v i s c e r a l regions and f o l l o w s the most p o s t e r i o r boundaries o f the v i s -c e r a l mass. The second loop ( F i g . 16a, LP 2) i s i s deeper i n p o s i t i o n and i s never v i s i b l e from the mantle s u r f a c e . I t i s l o c a t e d i n the c e n t r a l 70 regions of the v i s c e r a l c a v i t y j u s t to the r i g h t of the m i d l i n e , and i s c i r c u l a r i n shape. A f t e r completing loop 2 the r a d u l a passes a n t e r i o r l y again on the r i g h t s i d e o f the v i s c e r a l mass and terminates i n the r a d u l a r bulb p o s t e r i o r to the r i g h t s i d e o f the odontophore ( F i g . 16a, RB). I n d i v i d u a l v a r i a t i o n i n r a d u l a r c o n f i g u r a t i o n i s g r e a t e r i n t h i s s p e c i e s than i n the oth e r two. The r a d u l a r sheath v a r i e s i n l e n g t h p r o p o r t i o n a l to body s i z e ( d i s c u s s e d i n the next s e c t i o n under "Length of the Radula"), and i n the exact s i z e and p o s i t i o n of the lo o p s . The course which the r a d u l a f o l l o w s through the v i s c e r a l mass i s , however, almost always the same. Out of 60 animals examined, 56 had the d e s c r i b e d r a d u l a r c o n f i g u r a t i o n (=94%). The main element o f v a r i a t i o n i s found i n the s i z e o f loop 1. In some animals the loop a t t a i n s o n l y the m i d - v i s c e r a l r e g i o n s . In ot h e r s i t extends poste-r i o r l y to reach the most p o s t e r i o r boundary o f the v i s c e r a l c a v i t y . In some i n d i v i d u a l s the super-f i c i a l loop not o n l y a t t a i n s the p o s t e r i o r l i m i t , but curves t o the l e f t , passes a n t e r i o r l y and extends as f a r a n t e r i o r l y as the l e f t s i d e o f loop 2, l o -cated i n the m i d v i s c e r a l r e g i o n s . Loop 2 v a r i e s o n l y s l i g h t l y i n s i z e and i n p o s i t i o n . I t i s u s u a l l y l o c a t e d to the r i g h t o f the m i d l i n e , but o f t e n i s s i t u a t e d a t or s l i g h t l y 71 to the l e f t o f the m i d l i n e . The r a d u l a r bulb i s u s u a l l y l o c a t e d to the r i g h t o f the m i d l i n e , but o c c a s i o n a l l y may be found on the l e f t , o r i t may c r o s s over to the l e f t and then back again t e r m i n a t i n g on the r i g h t s i d e . Composite diagrams o f ten i n d i v i d u a l s a t each l o c a l i t y are shown i n F i g u r e s 19b, 20b, and 21b. As can be seen, the radulae extend to the extreme p o s t e r i o r r e g i ons o f the v i s c e r a l c a v i t y , occupying most of the p o s t e r i o r h a l f from the l e f t hand l i m i t to the r i g h t . S i nce there i s c o n s i d e r a b l e v a r i a t i o n i n the s i z e and placement of loop 1, the e x t e n t and p o s i -t i o n o f the p o r t i o n v i s i b l e from the mantle s u r f a c e v a r i e s from animal to animal ( F i g s . 19a, 20a, and 21a). I t i s always, however, l o c a t e d i n the p o s t e -r i o r regions of the v i s c e r a l c a v i t y on the extreme r i g h t hand s i d e , sometimes a l s o c u r v i n g around to the l e f t s i d e . Comparison o f the three p o p u l a t i o n s shows t h a t specimens from S t a n l e y Park f r e q u e n t l y possess a s h o r t e r s u p e r f i c i a l loop (loop 1) than those from B a m f i e l d or Bowen I s l a n d . T h i s loop extends most o f t e n o n l y to the m i d - v i s c e r a l r e g i o n s i n the S t a n l e y Park p o p u l a t i o n , while i n the other two p o p u l a t i o n s i t extends almost always to the p o s t e -r i o r r e g i o n s of the v i s c e r a l c a v i t y ( F i g s . 19b, 72 20b, and 21b) . b. C o l l i s e l l a scutum The r a d u l a i n t h i s s p e c i e s i s s h o r t e r ( r e -l a t i v e to body s i z e ) and the c o n f i g u r a t i o n l e s s complex than i n C. persona. A f t e r e n t e r i n g the v i s c e r a l c a v i t y , the r a d u l a r sheath makes a .sudden t u r n to the r i g h t , p a s s i n g a t near r i g h t angles t o the preceding p o r t i o n , and then moves to the l e f t again u n t i l i t a t t a i n s the approximate m i d l i n e . T h i s forms loop 1 ( F i g . 17a, LP 1). From the mid-l i n e the r a d u l a moves to the r i g h t and a n t e r i o r l y again i n a wide arc ( F i g . 17a, LP 2), t e r m i n a t i n g i n the r a d u l a r bulb p o s t e r i o r to the odontophore. A s m a l l p o r t i o n o f the r a d u l a i s o f t e n , but not always, v i s i b l e from the mantle s u r f a c e ( F i g . 17b). T h i s v i s i b l e s e c t i o n i s a p a r t o f the ascending p o r t i o n o f loop 2. I t i s a s h o r t e r s e c t i o n of r a d u l a than t h a t which i s v i s i b l e i n C. persona, and i s always l o c a t e d on the r i g h t s i d e i n the approximate m i d v i s c e r a l r e g i o n . As was found i n C. persona, d e s p i t e i n d i v i d u a l v a r i a t i o n i n loop s i z e and placement, the ge n e r a l p a t t e r n of r a d u l a r l o o p i n g i s always the same and the c o n f i g u r a t i o n i n t h i s s p e c i e s remains d i s -t i n c t from t h a t o f the oth e r two s p e c i e s . The r a d u l a v a r i e s mainly i n the shape and s i z e o f loop 1. In some i n d i v i d u a l s t h i s loop i s 73 not pronounced, and the radula veers only s l i g h t l y to the r i g h t of the midline. In other animals the loop i s exaggerated and the radula passes f a r to the r i g h t of the midline and sometimes also a n t e r i o r l y before curving p o s t e r i o r l y and retur-ning to the midline. The composite diagrams (Figs. 19d, 20d, and 2Id) show that the radula i s located within the anterior, mid, and post-mid regions of the v i s c e r -a l . mass, and that within t h i s area, most of the radula i s located at and to the r i g h t of the mid-l i n e . I t i s never found i n the most posterior regions of the v i s c e r a l cavity as i t i s i n C. persona. A portion of the radula i s often, but not always, v i s i b l e from the mantle surface. When v i s i b l e , v a r i a t i o n i s very s l i g h t (Figs. 19c, 20c, and 21c). Comparison of the three populations shows no notable difference i n radular configuration (Figs. 19d, 20d, and 21d). c. C o l l i s e l l a pelta After entering the v i s c e r a l cavity the ra-dula loops dorsally or to the r i g h t , passes ante-r i o r l y and terminates posterior to the odontophore i n the radular bulb (Fig. 18a). Thus, the radular configuration i n C. pelta consists of a single, 74 simple loop which never passes f a r t h e r p o s t e r i o r l y than the c e n t r a l r e g i o n o f the v i s c e r a l c a v i t y . No p o r t i o n s o f the r a d u l a are ever v i s i b l e from the s u r f a c e o f the mantle ( F i g . 18b). The e n t i r e s t r u c t u r e i s s i t u a t e d deep w i t h i n the v i s c e r a . The r a d u l a v a r i e s very l i t t l e i n r e l a t i v e l e n g t h , but some v a r i a t i o n does occur i n the exact placement and shape o f the loo p . As i n C. persona and C. scutum, while v a r i a t i o n o c c u r s , always the same c o n f i g u r a t i o n i s d i s p l a y e d . The loop may be s i t u a t e d j u s t t o the r i g h t of the m i d l i n e o r f a r to the r i g h t ; o c c a s i o n a l l y i t bends f i r s t t o the l e f t and then loops around to the r i g h t . Often there i s a l o c a l i z e d bend or "kink" on the v e n t r a l s i d e o f the loop; l e s s o f t e n there i s a bend a t the apex o r on the d o r s a l s i d e . The composite diagrams ( F i g s . 19f, 20f, and 21f) show t h a t the r a d u l a does not extend p o s t e r i o r to the m i d - v i s c e r a l r e g i o n and extends on l y s l i g h t l y to the r i g h t o f the m i d l i n e (not as f a r to the r i g h t as i n C. scutum). Comparison of the three p o p u l a t i o n s shows no n o t a b l e d i f f e r e n c e i n r a d u l a r c o n f i g u r a t i o n ( F i g s . 19f, 20f, and 2 1 f ) . 75 F i g u r e 16a. Photograph of a specimen of C o l l i s e l l a  persona which has been d i s s e c t e d to show the c o n f i g u r a t i o n o f the r a d u l a r sheath w i t h i n the v i s c e r a l c a v i t y . The d o r s a l mantle, gonad, d i g e s t i v e gland and gut have been removed. M a g n i f i c a t i o n approximately 6X. L P l , loop 1 of the r a d u l a ; LP2, loop 2 of the r a d u l a ; OD, odontophore; RB, r a d u l a r b u l b . F i g u r e 16b. Photograph of the above specimen p r i o r to d i s s e c t i o n . A p o r t i o n of the r a d u l a r sheath i s v i s i b l e beneath the d o r s a l mantle. L P l , loop 1 o f the r a d u l a . 77 F i g u r e 17a. Photograph of a specimen of C o l l i s e l l a  scutum which has been d i s s e c t e d to show the c o n f i g u r a t i o n o f the r a d u l a r sheath w i t h i n the v i s c e r a l c a v i t y . The d o r s a l mantle, gonad, d i g e s t i v e gland and gut have been removed. M a g n i f i c a t i o n approximately 6X. L P l , loop 1 of the r a d u l a ; LP2, loop 2 of the r a d u l a ; OD, odontophore; RB, r a d u l a r b u l b . F i g u r e 17b. Photograph o f the above specimen p r i o r to d i s s e c t i o n . A p o r t i o n of the r a d u l a r sheath i s v i s i b l e beneath the d o r s a l mantle. R, r a d u l a r sheath. OD RB LP 1 LP 2 79 F i g u r e 18a. Photograph o f a specimen o f C o l l i s e l l a  p e l t a which has been d i s s e c t e d to show the c o n f i g u r a t i o n o f the r a d u l a r sheath w i t h i n the v i s c e r a l c a v i t y . The d o r s a l mantle, gonad, d i g e s t i v e g l a n d and gut have been removed. M a g n i f i c a t i o n approximately 6X. OD, odontophore; R, r a d u l a ; RB, r a d u l a r b u l b . F i g u r e 18b. Photograph o f the above specimen p r i o r to d i s s e c t i o n . The r a d u l a r sheath i s not v i s i b l e be-neath the d o r s a l mantle. 81 F i g u r e 19. Composite diagrams o f 10 i n d i v i d u a l s o f each s p e c i e s c o l l e c t e d from B a m f i e l d showing the v a r i a -t i o n i n r a d u l a r c o n f i g u r a t i o n ; (a) C. persona p r i o r to d i s -s e c t i o n , (b) C. persona a f t e r removal o f the v i s c e r a , (c) C. scutum p r i o r t o d i s s e c t i o n , (d) C. scutum a f t e r removal of the v i s c e r a , (e) C. p e l t a p r i o r to d i s s e c t i o n , (f) C. p e l t a a f t e r removal o f the v i s c e r a . M a g n i f i c a t i o n 1.5 t o 5X. OD, odontpphore; R, r a d u l a . C.persona R C. scutum C. pelta 83 F i g u r e 20. Composite diagrams o f 10 i n d i v i d u a l s of each s p e c i e s c o l l e c t e d from St a n l e y Park showing the v a r i a t i o n i n r a d u l a r c o n f i g u r a t i o n ; (a) C. persona p r i o r to d i s s e c t i o n , (b) C. persona a f t e r removal o f the v i s c e r a , (c) C. scutum p r i o r t o : - d i s s e c t i o n , (d) C. scutum a f t e r removal o f the v i s c e r a , (e) C. p e l t a p r i o r to d i s s e c t i o n , (f) C. p e l t a a f t e r removal of the v i s c e r a . M a g n i f i c a t i o n 1.5 to 5X. OD, odontophore; R, r a d u l a . 85 Figure 21. Composite diagrams of 10 individuals of each species co l l e c t e d from Bowen Island showing the v a r i a t i o n i n radular configuration; (a) C. persona p r i o r to dissection, (b) C. persona a f t e r removal of the viscera, (c) C. scutum p r i o r to dissection, (d) C. scutum a f t e r removal of the v i s -cera, (e) C. pelta p r i o r to dissection, (f) C. pelta a f t e r removal of the viscera. Magnification 1.5 to 5X. OD, odontophore; R, radula. R C. persona R C. scutum C. pelta 87 5. Length o f the Radula F i g u r e 22 shows the r e l a t i o n s h i p between r a d u l a r l e n g t h and wet weight o f s o f t p a r t s f o r C. persona, C. scutum, and C. p e l t a . Log/log p l o t s y i e l d a s t r a i g h t l i n e . The form of the equations given i s : Log RL = C + BlogWW where RL = r a d u l a r l e n g t h WW = wet weight o f s o f t p a r t s C = i n t e r c e p t B = slope of the l i n e . The equations f o r the l i n e s d e s c r i b i n g the r e l a t i o n -s h i p between r a d u l a r l e n g t h and wet weight are as f o l l o w s : C. persona Log RL = 1.720 + 0.2649LogWW N=49 C. scutum Log RL = 1.571 + 0.270lLogWW N=50 C. p e l t a Log RL = 1.378 + 0.2607LogWW N=51 The r e g r e s s i o n s are s i g n i f i c a n t a t P=0.01. A n a l -y s i s o f cov a r i a n c e r e v e a l s t h a t the slop e s o f the l i n e s are not s i g n i f i c a n t l y d i f f e r e n t among the three s p e c i e s . The C value s ( i n t e r c e p t s ) are, however, d i f f e r e n t . For any given wet weight, then, the radu-l a r l e n g t h o f C. persona i s s i g n i f i c a n t l y g r e a t e r than t h a t o f C. scutum, and t h a t o f C. scutum i s s i g n i f i -c a n t l y g r e a t e r than t h a t o f C. p e l t a . At a wet weight o f 1 g, f o r example, i n d i v i d u a l s o f C. persona would have a r a d u l a r l e n g t h o f 52 mm, i n d i v i d u a l s o f C. scutum 37 mm, and i n d i v i d u a l s o f C. p e l t a 24 mm. 88 There i s good s e p a r a t i o n o f the p o i n t s along a l l three l i n e s w i t h very l i t t l e o v e r l a p between the s p e c i e s , even a t very low wet weights. F i g u r e 23 shows the r e l a t i o n s h i p between r a d u l a r l e n g t h and s h e l l l e n g t h f o r the same samples as are shown i n F i g u r e 22. A r i t h m e t i c p l o t s y i e l d a s t r a i g h t l i n e . The equations are of the form: RL = C + B X SL where RL = r a d u l a r l e n g t h SL = s h e l l l e n g t h C = i n t e r c e p t B = slope o f the l i n e The equations o f the l i n e s are as f o l l o w s : C. persona RL = 3.401 + 1.794 SL N=49 C. scutum RL = 4.794 + 0.9702 SL N=50 C. p e l t a RL = 1.571 + 0.8587 SL N=51 The r e g r e s s i o n s are s i g n i f i c a n t a t P=0.01. While the s l o p e s o f the l i n e s o f C. scutum and C. p e l t a are not s i g n i f i c a n t l y d i f f e r e n t , t h a t o f C. persona i s s i g n i f i c a n t l y d i f f e r e n t from those of the ot h e r two s p e c i e s . The i n t e r c e p t s o f the r e g r e s s i o n l i n e s o f C. persona and C. scutum are not s i g n i f i c a n t l y d i f f e r -ent. The i n t e r c e p t s o f the l i n e s f o r C. scutum and C. p e l t a are not s i g n i f i c a n t a t P=0.01, but are s i g n i f i c a n t a t P=0.05. There e x i s t s a s i m i l a r r e l a -t i o n s h i p here as f o r r a d u l a r l e n g t h and wet weight, i n t h a t f o r any given s h e l l l e n g t h the r a d u l a r l e n g t h 89 of C. persona i s g r e a t e r than t h a t of C. scutum, and t h a t o f C. scutum i s g r e a t e r than t h a t of C. p e l t a . T h i s r e l a t i o n s h i p i s , however, l e s s d i s t i n c t among the s m a l l e r animals, (animals l e s s than 25 mm i n s h e l l l e n g t h ) , p a r t i c u l a r l y among i n d i v i d u a l s of C. scutum and C. p e l t a . W i t h i n the range o f 10 to 25 mm s h e l l l e n g t h there i s c o n s i d e r a b l e o v e r l a p o f p o i n t s be-tween these two s p e c i e s . The independent v a r i a b l e s i n F i g u r e s 22 and 23 i n d i c a t e t o t a l animal s i z e , and p r o v i d e a b a s i s f o r comparison o f r a d u l a r lengths among the three s p e c i e s . Wet weight i s c o n s i d e r e d to be a more accurate i n d i -c a t o r o f animal s i z e than i s s h e l l l e n g t h , s i n c e weight, b e i n g p r o p o r t i o n a l to volume, accounts f o r s i z e measurement of the animal i n three dimensions, i e . width, l e n g t h and h e i g h t . S h e l l l e n g t h accounts f o r s i z e measurement i n one dimension. Using o n l y the l e n g t h as an i n d i c a t o r o f s i z e may l e a d t o erroneous i n t e r p r e t a t i o n s o f the r e s u l t s . In C. scutum, f o r example, there i s a tendency f o r the animal to i n c r e a s e g r e a t l y i n s h e l l l e n g t h as i t grows but r e l a t i v e l y l i t t l e i n s h e l l h e i g h t , r e s u l t i n g i n a very f l a t t e n e d s h e l l . In C. p e l t a , however, there i s a tendency to i n c r e a s e g r e a t l y i n s h e l l h e i g h t but r e l a t i v e l y l i t t l e i n s h e l l l e n g t h , r e s u l t i n g i n a very e l e v a t e d s h e l l w i t h a reduced a p e r t u r e . These d i f f e r -ences have been shown to be a d a p t a t i o n s to d e s i c c a t i o n 90 between high and low i n t e r t i d a l limpets (Orton, 1933; Moore, 1934; Segal, 1956; Seapy and Hoppe, 1973; Bannister, 1975). The r e s u l t i s that, i f only s h e l l lengths are used as size indicators, radular lengths of C. scutum tend to be minimized while those of C. pelta tend to be maximized, pushing the regression l i n e s closer together. Thus, the greater overlap of points between these species i n Figure 23. This d i f f e r e n t i a l growth rate i n the dimensions of height and length also results i n vastly d i f f e r e n t sample means i n the two species (the mean s h e l l length for C. scutum i s 26.1 mm; that of C. pelta i s 18.5 mm). Another source of error i n the measurement of s h e l l length i s that of damage to the s h e l l margins i n the form of chipping, breaking, and erosion, which i s frequently found i n the sh e l l s of both C. scutum and C. pelta. Shell damage, of course, does not a f f e c t the measurement of wet weight. The plots of radular length versus s h e l l length show that the slope of the l i n e for C. persona i s greatly d i f f e r e n t from that of the other two species, i n d i c a t i n g an increased growth rate of the radula r e l a t i v e to the s h e l l length i n thi s species. The plots using wet weight as the independent variable do not r e f l e c t this d i f f e r e n t i a l growth rate, implying that the difference i s due to s h e l l growth in the length dimension and not to body growth as a whole 91 i n t h i s s p e c i e s . Slopes of the wet weight p l o t s are, i n f a c t , a l l p r a c t i c a l l y e q u a l , i n d i c a t i n g t h a t there i s a s i m i l a r growth r a t e o f the r a d u l a r e l a t i v e to wet weight o f the s o f t p a r t s f o r a l l three s p e c i e s . I t i s suggested, t h e r e f o r e , t h a t the wet weight more c l e a r l y c h a r a c t e r i z e s the r e l a t i o n s h i p between r a d u l a r l e n g t h and animal s i z e than does the s h e l l l e n g t h , s i n c e t h i s measurement i s l e s s l i k e l y to r e -f l e c t d i f f e r e n c e s between s p e c i e s which are due s o l e l y to environmental e f f e c t s . 92 Figure 22. Regression of radular length as a function of wet weight of s o f t parts i n three species of limpets from Bowen Island, B r i t i s h Columbia. Each point represents an i n d i v i d u a l . • = C o l l i s e l l a persona; O = C o l l i s e l l a scutum; • = C o l l i s e l l a p e l t a Wet Weight of Soft Parts (gms) 94 Figure 23. Regression of radular length as a function of s h e l l length i n three species of limpets from Bowen Island, B r i t i s h Columbia. Each point represents an i n d i v i d u a l . • = C o l l i s e l l a persona; O = C o l l i s e l l a p e l t a = C o l l i s e l l a scutum; 95 Shell Length (mm) 96 B. Morphology o f the Jaw In C o l l i s e l l a s p e c i e s there i s a s i n g l e symmetrical jaw (= mandible) with f o u r w i n g - l i k e e x t e n s i o n s . I t i s a c h i t i n o u s s t r u c t u r e , l o c a t e d w i t h i n the b u c c a l c a v i t y an-t e r o - d o r s a l to the o r a l tube. The s t r u c t u r e i s concave i n shape, a l l o w i n g i t to f i t c l o s e l y a g a i n s t the rounded a n t e r i o r edge o f the b u c c a l c a v i t y . The p o s i t i o n of the jaw r e l a t i v e to o t h e r s t r u c t u r e s of the b u c c a l c a v i t y i n C o l l i s e l l a i s given by Walker (1968), and diagrammed f o r P a t e l l a by Runham and Thornton (1967). Small dense bun-d l e s of muscles are a t t a c h e d to the d o r s a l and v e n t r a l s u r f a c e s of the jaw, which run to the body w a l l and buc-c a l mass. D e t a i l s o f jaw musculature i n P a t e l l a are d i s -cussed i n Graham (1964). With each r a d u l a r p u l s a t i o n the jaw i s p r o t r u d e d through the o r a l tube, forming a b a r r i e r between the a n t e r i o r and l a t e r a l r e g i o n s o f the mouth, and the o u t e r l i p s . The jaw f u n c t i o n s not i n the c o l l e c -t i o n o f food, as has o f t e n been supposed, but i n the con-t r o l o f the r a d u l a r t e e t h and the b u c c a l mass d u r i n g f e e d i n g (Graham, 1964). 1. Shape of the A n t e r i o r Band In C. persona the median area o f the a n t e r i o r band i s always p e r f e c t l y even and smooth ( F i g . 24c). The a n t e r i o r margins o f the jaws o f C. scutum tend o f t e n to be s l i g h t l y uneven i n the median area ( F i g . 24b), but i n some specimens are smooth as i n C. per-sona. In C. p e l t a there i s a pronounced median "beak" 97 which extends along the l o n g i t u d i n a l a x i s o f the jaw i n the median area of the a n t e r i o r band to the d o r s a l l i n e o f f u s i o n ( F i g . 24a). I t i s r a i s e d d o r s a l l y from the r e g u l a r c o n c a v i t y of the d o r s a l s u r f a c e , and pro-j e c t s a n t e r i o r l y from the a n t e r i o r margin. A s i m i l a r beak has been observed i n specimens o f C. i n s e s s a (Walker, 1968) . 2. Grooving of the V e n t r a l Surface Grooves or r i d g e s occur i n the jaws of some C o l l i s e l l a s p e c i e s along the v e n t r a l s u r f a c e i n the median area of the a n t e r i o r band. The e x t e n t o f grooving was found to d i f f e r among the three s p e c i e s s t u d i e d . In C. p e l t a ( F i g s . 25a and 25b) c l e a r , o r -dered grooves were found along the v e n t r a l s u r f a c e of the median beak, s i m i l a r i n s t r e n g t h to those shown f o r P a t e l l a v u l g a t a (Runham and Thornton, 1967). These grooves were e v i d e n t i n every specimen examined. The two c e n t r a l grooves are probably made by the i n n e r l a t e r a l s of the r a d u l a . These are the deepest and l o n g e s t grooves, extending p r a c t i c a l l y the e n t i r e l e n g t h o f the jaw. They are p a r a l l e l to each ot h e r and to the a n t e r o - p o s t e r i o r a x i s o f the jaw ( F i g . 25b). The two s e t s o f grooves immediately l a t e r a l to the c e n t r a l grooves are probably made by the med-i a n and o u t e r l a t e r a l s . These grooves, s i t u a t e d c l o s e l y together, are not as deep as those made by the i n n e r l a t e r a l t e e t h and are o n l y h a l f as long. 98 They are presen t o n l y a n t e r i o r l y . P a r a l l e l to each ot h e r , the two u s u a l l y occur a t an angle o f a p p r o x i -mately 5 degrees to the c e n t r a l grooves. One or two i n d i s t i n c t and very f a i n t grooves are o f t e n found l a t e r a l to those made by the out e r l a t e r a l s . These may be produced by the u n c i n i . They are a l s o p r e s e n t o n l y a n t e r i o r l y and u s u a l l y are s h o r t e r than the o t h e r grooves. Some f a i n t , i n d i s t i n c t grooving i s u s u a l l y ob-served on the jaws o f C. scutum, but the groove depth i n t h i s s p e c i e s i s never as g r e a t as t h a t found i n C. p e l t a ( F i g . 26a). The r i d g e s are l o c a t e d i n the c e n t r a l r e g i o n o f the a n t e r i o r band (as i n C. p e l t a ) , but never reach the e n t i r e l e n g t h o f the band, b e i n g u s u a l l y c o n f i n e d to the a n t e r i o r h a l f o n l y . Often the grooves are a l l o f equal depth, but o c c a s i o n a l l y the two c e n t r a l grooves are s l i g h t l y deeper. Those grooves l a t e r a l to the c e n t r a l s may be n e a r l y p a r a l l e l o r a t a s l i g h t i n c l i n a t i o n (two to three degrees) to the c e n t r a l grooves. In a l l but one o f the twenty specimens o f C. persona examined there was no grooving on the v e n t r a l s u r f a c e o f the a n t e r i o r band ( F i g . 26b). In the one jaw which had some f a i n t grooving, two c e n t r a l r i d g e s were e v i d e n t , and these were extremely weak, o c c u r r i n g o n l y on the a n t e r i o r h a l f o f the band. 99 The s t r e n g t h o r depth of grooving i n the three s p e c i e s d e s c r i b e d above appears to be c o r r e l a t e d w i t h the degree of sharpness of the t i p s o f the r a d u l a r t e e t h . In C. p e l t a , where the t e e t h are extremely curved and sharp- p o i n t e d a t the t i p s , jaw grooves are deep and d i s t i n c t . The r a d u l a r t e e t h o f C. scutum are much l e s s curved and p o i n t e d a t the t i p s than those of C. p e l t a . The jaw o f t h i s s p e c i e s bears c o r r e s p o n d i n g l y f a i n t e r and l e s s d i s t i n c t grooving. In C. persona, where the r a d u l a r t e e t h are s t r a i g h t and extremely b l u n t a t the t i p s , the v e n t r a l s u r f a c e of the jaw i s unmarked. The grooves due to the median and o u t e r l a t e r a l s i n C. p e l t a and some specimens of C. scutum are a t a s l i g h t angle to those o f the i n n e r l a t e r a l s and occur o n l y on the a n t e r i o r h a l f o f the band. T h i s i n d i c a t e s (as f o r the l a t e r a l and dominant t e e t h o f P a t e l l a  v u l g a t a , " Runham and Thornton, 1967) t h a t when the r a d u l a i s h e l d a g a i n s t the jaw the i n n e r l a t e r a l t e e t h move with l i t t l e d i v e r gence. The median and out e r l a t e r a l s , however, when s i t u a t e d p o s t e r i o r l y are a t a lower l e v e l than the i n n e r l a t e r a l s , becoming e r e c t and d i v e r g i n g very s l i g h t l y as they move a n t e r i o r l y . 100 Figure 24. Scanning electron micrographs showing the dorsal surface of the jaw. Magnification approximately 50X. (a) C. pelta, note the pronounced beak i n the median area of the anterior band, (b) C. scutum, the anterior band i s s l i g h t l y uneven, (c) C. persona, the anterior band i s smooth. A, anterior; P, posterior. 102 F i g u r e 25. Scanning e l e c t r o n micrographs showing the v e n t r a l s u r f a c e o f the jaw of C o l l i s e l l a p e l t a . Note the deep grooving i n the c e n t r e of the a n t e r i o r band; (a) M a g n i f i c a t i o n . a p p r o x i m a t e l y 50X, (b) M a g n i f i c a t i o n a p p r o x i -mately 10 OX. A, a n t e r i o r ; P, p o s t e r i o r . 103 104 F i g u r e 26. Scanning e l e c t r o n micrographs showing the v e n t r a l s u r f a c e of the jaw. M a g n i f i c a t i o n approximately 50X. (a) C. scutum, some f a i n t grooving i s e v i d e n t i n the median r e g i o n s , (b) C. persona, the s u r f a c e i s smooth and unmarked. A, a n t e r i o r ; P, p o s t e r i o r 106 C. Morphology o f the Gut and Rel a t e d S t r u c t u r e s 1. Gross Morphology i . Looping o f the Gut In a l l C o l l i s e l l a s p e c i e s the stomach and i n t e s t i n e make a s e r i e s o f complex loops through the v i s c e r a l mass, winding back and f o r t h among the d i g e s t i v e gland tubules and r a d u l a r sheath. As was found f o r other C o l l i s e l l a s p e c i e s (Walker, 1968), there i s a gen e r a l c h a r a c t e r i s t i c i n t e s t i n a l loop p a t t e r n f o r a l l the s p e c i e s s t u d i e d . W i t h i n t h i s g e n e r a l loop p a t t e r n , there are v a r i a t i o n s i n the exact placement and s i z e o f loops which are c h a r a c t e r i s t i c of each s p e c i e s . There e x i s t s , however, c o n s i d e r a b l e i n d i v i d u a l v a r i a t i o n i n t h i s p a t t e r n , such t h a t some o v e r l a p o f loop s i z e and placement among the three s p e c i e s was observed. The g e n e r a l course o f the d i g e s t i v e t r a c t f o r the three s p e c i e s i s s i m i l a r to t h a t des-c r i b e d i n oth e r C o l l i s e l l a s p e c i e s ( R i g h i , 1966; Walker, 1968). I t i s shown i n F i g u r e s 27 and 28. The esophagus passes p o s t e r i o r l y from the head r e g i o n i n the approximate m i d l i n e . At the l e v e l o f the p o s t e r i o r regions o f the midesophagus, the gut g r a d u a l l y begins to move across to the r i g h t s i d e o f the v i s c e r a l c a v i t y . I t narrows c o n s i d e r a b l y as the p o s t e r i o r esophagus i s 107 reached. The p o s t e r i o r esophagus widens i n t o a s h o r t expanded chamber, the p r o v e n t r i c u l u s , which i s separated from the stomach by a s t r o n g con-s t r i c t i o n . The duct o f the d i g e s t i v e gland en-t e r s the gut lumen near the j u n c t i o n o f the pro-v e n t r i c u l u s and the stomach, on the d o r s a l o r l e f t l a t e r a l w a l l . The stomach completely en-c i r c l e s the v i s c e r a l mass, p a s s i n g p o s t e r i o r l y from i t s p o i n t of j u n c t i o n w i t h the p r o v e n t r i -c u l u s and l o o p i n g around to the l e f t o f the v i s -c e r a l mass ( F i g . 27). I t passes a n t e r i o r l y , a t t a i n i n g the most a n t e r i o r l i m i t of the d i g e s t i v e gland, then loops to the r i g h t and passes pos-t e r i o r l y a g a i n . The stomach passes i n t o the i n -t e s t i n e as the lumen narrows. The e n t i r e s t r u c -t u r e l i e s i n one plane (as i n L o t t i a g igantea, F i s c h e r , 1904) and the d o r s a l w a l l i s p a r t i a l l y covered by tubules o f the d i g e s t i v e gland. A double r i d g e and groove run along the v e n t r o -l a t e r a l stomach w a l l and continue through p a r t o f the i n t e s t i n e . These have been d e s c r i b e d i n o t h e r C o l l i s e l l a s p e c i e s ( R i g h i , 1966) and i n P a t e l l a v u l g a t a (Graham, 1932; 19 49), and pro-bably r e p r e s e n t reduced t y p h l o s o l e s w i t h the i n t e s t i n a l groove. The stomach l a c k s the caecum, g a s t r i c s h i e l d and s t y l e sac which are found i n 108 F i g u r e 2 7a. Photograph of a specimen o f C o l l i s e l l a  persona d i s s e c t e d to show a p o r t i o n of the a l i m e n t a r y c a n a l . The esophagus, stomach and p o r t i o n s o f the i n t e s t i n e can be seen. M a g n i f i c a t i o n approximately 5X. F i g u r e 2 7b. Diagram of the above photograph. AE, a n t e r i o r esophagus; DDG, duct o f the d i g e s t i v e gland; DSG, duct o f the s a l i v a r y gland; EG, esophageal gland; G, gonad; H, he a r t ; LPA, loop A of the i n t e s t i n e ; LPB, loop B o f the i n t e s t i n e ; LPD, loop D o f the i n t e s t i n e ; LPE, loop E of the i n t e s t i n e ; ME, midesophagus; PE, p o s t e r i o r esophagus; PR, p r o v e n t r i c u l u s ; RT, rectum; S, stomach. 110 F i g u r e 28. Diagrams showing the course of the stomach, i n t e s t i n e , and rectum i n each o f the t h r e e s p e c i e s . Exact placement and s i z e of loops i s s u b j e c t to v a r i a t i o n w i t h i n each s p e c i e s . The g e n e r a l trends are shown; (a) C. p e l t a , (b) C. scutum, (c) C. persona. RT, rectum; S, stomach. 112 many o t h e r gastropods ( R i g h i , 19 66). The i n t e s -t i n e makes a s e r i e s of f i v e loops through the v i s -c e r a l mass, then e n t e r s the mantle c a v i t y as i t passes i n t o the rectum. The f i r s t loop of the i n t e s t i n e (loop A) c i r c l e s to the l e f t and passes a n t e r i o r l y , l y i n g deep i n the v i s c e r a l mass ( F i g s . 27 and 28). I t c i r c l e s to the r i g h t as the an-t e r i o r loop o f the stomach i s reached, and makes a wide arc along the stomach perimeter p a s s i n g p o s t e r i o r l y again. The a n t e r i o r and.des-"' cending p o r t i o n s of t h i s loop are sometimes v i s i b l e to the r i g h t of the stomach, and the w a l l s are o f t e n , but not always, pigmented a much darker c o l o u r than the r e s t of the i n t e s t i n e i n a l l three s p e c i e s . Pigmentation c o l o u r v a r i e s from green to dark brown or b l a c k . The second loop o f the i n t e s t i n e (loop B) begins as the i n t e s t i n e moves again to the l e f t , p a s s i n g be-neath the stomach. I t moves a n t e r i o r l y , deep i n the v i s c e r a l mass, p a s s i n g beneath the most an-t e r i o r loop of the stomach and loop A, a t t a i n i n g the rectum. From t h i s p o i n t i t turns s h a r p l y to the l e f t i n C. persona and C. scutum, and u s u a l l y s h a r p l y to the r i g h t i n C. p e l t a , then passes p o s t e r i o r l y and to the l e f t (marking loop C). The i n t e s t i n e passes p o s t e r i o r l y , f o l l o w i n g c l o s e l y the rectum and adjacent p o r t i o n o f i n t e s t i n e , 113 l y i n g v e n t r a l and j u s t to the r i g h t o f these s t r u c t u r e s . The gut g r a d u a l l y c r o s s e s over to the r i g h t s i d e o f the v i s c e r a l mass near the l e v e l of the p r o v e n t r i c u l u s . T h i s c r o s s marks the b e g i n -n i n g o f loop D. The i n t e s t i n e passes beneath the stomach and curves p o s t e r i o r l y again as the d i s t a l stomach w a l l i s a t t a i n e d . The gut loops to the l e f t (marking loop E) and passes a n t e r i o r -l y , s t i l l f o l l o w i n g the d i s t a l stomach w a l l . The i n t e s t i n e ends where i t e n t e r s the mantle c a v i t y . The rectum c r o s s e s over to the r i g h t o f the mantle c a v i t y e n c l o s e d w i t h i n a p a p i l l a , t e r m i n a t i n g i n the anus. The placement o f the p r o v e n t r i c u l u s w i t h r e s p e c t to the p o s t e r i o r esophagus and the s t o -mach d i f f e r s i n the three s p e c i e s s t u d i e d . These d i f f e r i n g s p a t i a l r e l a t i o n s h i p s are shown i n F i g u r e 29. In a l l three s p e c i e s the p o s t e r i o r esophagus approaches the stomach from the l e f t s i d e . In C.. pelta,. the p r o v e n t r i c u l u s i s s i t -uated v e n t r a l to the stomach and e n t e r s the s t o -mach v i a a c o n s t r i c t e d channel from the v e n t r a l s i d e . In C. scutum, the p r o v e n t r i c u l u s i s s i t -uated to the l e f t o f the stomach, always e n t e r i n g by a c o n s t r i c t e d channel, from the l e f t s i d e . In C. persona the expansion o f the p r o v e n t r i c u l u s i s s i t u a t e d a n t e r i o r to the stomach, and e n t e r s the 114 F i g u r e 29. Diagrams showing the placement of the p r o v e n t r i c u l u s r e l a t i v e to the stomach and p o s t e r i o r esophagus i n each o f the three s p e c i e s ; (a) C. p e l t a , d o r s a l and v e n t r a l views; (b) C. scutum, d o r s a l view, (c) C. persona, d o r s a l view, DDG, duct of the d i g e s t i v e gland; PE, p o s t e r i o r esophagus; PR, p r o v e n t r i c u l u s ; S, stomach. 115 b PR C. persona c 116 stomach from the a n t e r i o r s i d e . T h i s c h a r a c t e r was found to be c o n s i s t e n t . Each animal examined d i s p l a y e d the p r o v e n t r i c u l u s placement charac-t e r i s t i c o f i t s s p e c i e s . The stomach diameter i n C. p e l t a i s c o n s i d -.erabiy g r e a t e r than t h a t o f C. scutum and C. per-sona ( F i g s . 28a, 28b, and 28c). T h i s , too i s a c o n s i s t e n t d i f f e r e n c e and was found i n every specimen examined, whether the gut was f u l l o r empty. Walker (1968) a l s o noted g r e a t e r stomach diameters i n some o f the C o l l i s e l l a s p e c i e s she s t u d i e d . Her diagrams r e f l e c t the s i z e d i f f e r -e n c e between the stomachs o f C. p e l t a and C. scutum (C. persona was not i n c l u d e d i n her study o f gut morphology), c o n f i r m i n g the presen t f i n d -i n g . She found, a l s o , t h a t the stomach of C. p e l t a o f t e n c o n t a i n e d s i z e a b l e fragments o f l a r g e r algae, w h i l e the guts o f C. scutum and C. l i m a t u l a c o n t a i n e d o n l y much s m a l l e r fragments. T h i s was found a l s o i n C. p e l t a and C. scutum i n the p r e s e n t study. Gut contents o f C. persona resembled those o f C. scutum i n s i z e . Some s p e c i e s d i f f e r e n c e s among C. p e l t a , C. persona, and C. scutum e x i s t i n the s i z e and placement of i n t e s t i n a l loops. These may b e s t be c o n s i d e r e d , however, as trends r a t h e r than s t r i c t l y as d i a g n o s t i c f e a t u r e s , s i n c e c o n s i d e r -117 able i n d i v i d u a l v a r i a t i o n and some s p e c i e s over-la p was observed. The ge n e r a l trends are shown i n F i g u r e s 2 8a, 2 8b, and 2 8c, and are as f o l l o w s . The b e g i n n i n g o f loop A i s .usually; s i t u a t e d f a r -t h e r a n t e r i o r l y i n C. p e l t a than i n C. scutum and C. persona. Loop B tends t o be s m a l l e r and more a n t e r i o r l y s i t u a t e d i n C. persona than C. p e l t a and C. scutum. Loop C u s u a l l y passes f a r t h e r a n t e r i o r l y i n C. p e l t a than i n the ot h e r two s p e c i e s . In C. scutum and C. persona t h i s loop does not pass a n t e r i o r t o the rectum, whereas i n C. p e l t a i t almost always passes a n t e r i o r to t h a t s t r u c t u r e , l y i n g deep i n the v i s c e r a l c a v i t y . In a d d i t i o n , w h i l e loop C makes a marked t u r n t o the l e f t i n both C. persona and C. scutum, i t u s u a l l y turns to the r i g h t i n C. p e l t a . In t h i s s p e c i e s i t passes p o s t e r i o r l y and then to the l e f t , c r o s s i n g over on i t s e l f and forming an a d d i t i o n a l loop. In the o t h e r two s p e c i e s t h i s loop i s never found. T h i s d i f f e r e n c e i s not shown i n Walker's (1968) diagrams o f the gut loops i n C. p e l t a and C. scutum. Walker's (1968) g e n e r a l i z e d diagram of the d i g e s t i v e t r a c t o f C o l l i s e l l a i s s i m i l a r to t h a t o f the three s p e c i e s s t u d i e d here i n l e n g t h and placement o f the i n t e s t i n a l loops w i t h the ex-c e p t i o n o f two major f e a t u r e s . In a l l her 118 diagrams of gut looping of C o l l i s e l l a species (including those of C. pelta and C. scutum) the descending portion of loop A (= loop 1) i s s i t -uated far to the l e f t towards the central v i s -c e r al regions. In the three species studied here, the descending portion of loop A i s never situated on the l e f t , but i s always found on the extreme ri g h t hand l i m i t of the v i s c e r a l mass. Further, the portion of intestine v i s i b l e a n t e r i o r l y and to the r i g h t , making a wide arc around the most .anterior portion of the stomach i n Walker's diagrams i s shown to be the ascending portion of loop B (= loop 2). In C. pelta, C. persona, and C. scutum t h i s v i s i b l e portion of the i n t e s t i n e i s always the descending portion of loop A (= loop 1). i i . Relative Size of Salivary Glands The general placement and arrangement of the sali v a r y glands (= anterior sal i v a r y glands; buc-c a l glands) i n C o l l i s e l l a has been discussed by Righi (1966), Walker (1968), and by Fretter and Graham (1962). B r i e f l y described, they are a p a i r of glands, the main mass of which i s located i n the anterior portion of the v i s c e r a l cavity. Each gland empties into the buccal cavity by a long duct which passes an t e r i o r l y l a t e r a l to the anterior esophagus (Fig. 30). In the region of 119 the anterior buccal cavity the ducts move yen--, t r a i l y and obliquely towards the midline, passing through the dorsal folds and emptying into the lumen of the buccal cavity. As was found for Acmaea (=Collisella) subrugosa (Righi, 1966), the glands are asymmetrical. The ri g h t i s broader than i t i s long, l y i n g to the r i g h t and a l i t t l e above the r i g h t l a t e r a l pouch. The l e f t gland i s longer than i t i s broad, being p a r t i a l l y covered by the l e f t l a t e r a l pouch and posterior esophagus, and bounded v e n t r a l l y and on the l e f t by the gonad. The size and extent of the main mass of the glands d i f f e r s i n the three species investigated. The structure i s much larger i n C. pe l t a than i t i s i n either of the other two species (Figs. 30, 31, and 32). Both the glands are much greater i n extent than those which have been shown for C. pelta (Walker, 1968). The ducts pass into the glands at about the l e v e l of the beginning of torsion of the midesophagus. At the l e v e l of approximately 90 degrees torsion of the midgut the r i g h t s a l i v a r y gland has elaborated greatly both dorso-ventrally and l a t e r a l l y such that p r a c t i c a l l y the entire central and right-hand regions of the v i s c e r a l cavity are occupied by the s a l i v a r y gland. At t h i s l e v e l , the extent of the l e f t gland i s l i m i t e d on the l e f t by the 120 gonad and on the r i g h t by the midesophagus, r e -s u l t i n g i n d o r s o - l a t e r a l e l a b o r a t i o n but very l i t t l e l a t e r a l expansion. Tubules from both the r i g h t and the l e f t glands pass d o r s a l l y and a l s o v e n t r a l l y a c r o s s the l a t e r a l pouches, completely e n c i r c l i n g the midesophagus i n t h i s r e g i o n ( F i g . 30). The r i g h t gland diminishes i n s i z e as the more p o s t e r i o r v i s c e r a l r e g i o ns are reached. As the midesophagus c r o s s e s to the r i g h t o f the v i s c e r a l c a v i t y , the l e f t gland e l a b o r a t e s s u r -rounding loops D and E o f the i n t e s t i n e . The l e f t s a l i v a r y gland g r a d u a l l y d i m i n i s h e s to the c e n t r a l r e g i o ns o f the v i s c e r a l mass as i t passes p o s t e r i o r l y , s t i l l c l o s e l y a s s o c i a t e d with the midesophagus.. I t terminates j u s t p o s t e r i o r to loop D o f the i n t e s t i n e . Though i n C. scutum the s a l i v a r y glands occupy a s i m i l a r p o s i t i o n w i t h i n the v i s c e r a l c a v i t y i n r e l a t i o n t o o t h e r s t r u c t u r e s , the s i z e and e x t e n t o f the main mass o f each gland i s c o n s i d e r a b l y l e s s than i n C. p e l t a ( F i g . 31). In the r e g i o n o f 90 degrees t o r s i o n , a p o r t i o n of the gl a n d reaches d o r s a l l y over the r i g h t l a t e r a l pouch o f the midesophagus. Rarely, however, do the tubules o f the r i g h t and l e f t glands become i n t e r m i n g l e d d o r s a l l y and v e n t r a l l y to e n c l o s e the midgut as they do i n C. p e l t a . The l e f t 121 gland does not e l a b o r a t e l a t e r a l l y as i t does i n C. p e l t a , and n e i t h e r the l e f t nor the r i g h t glands pass as f a r p o s t e r i o r l y . The main masses o f the s a l i v a r y glands i n C. persona are l o c a t e d i n a s i m i l a r p o s i t i o n t o those o f C. scutum and are o n l y s l i g h t l y s m a l l e r i n s i z e ( F i g . 32). P o s t e r i o r to the l e v e l o f 90 degrees t o r s i o n the l e f t gland becomes reduced to o n l y a few t u b u l e s which continue f o r a s h o r t d i s t a n c e p o s t e r i o r l y , c l o s e l y a p p l i e d to the r i g h t eso-phageal w a l l . Some i n d i v i d u a l v a r i a t i o n was found w i t h i n the three s p e c i e s i n the l a t e r a l e x t e n t o f the glands. The minimum ext e n t of each gland i s r e -presented i n F i g u r e s 30, 31, and 32 w i t h d o t t e d l i n e s . V a r i a t i o n was noted o n l y i n those regions represented w i t h d o t t e d l i n e s , and appeared to be r e l a t e d to the s i z e o f the gonad ( i e . i n those animals i n which the gonad was g r e a t l y e n l a r g e d , there was some displacement of the s a l i v a r y glands, both d o r s a l l y and toward the m i d l i n e ) . Morphology o f the D i g e s t i v e Gland Tubules The d i g e s t i v e gland i s the l a r g e s t gland a s s o c i a t e d w i t h the a l i m e n t a r y system. I t i s a compound t u b u l a r gland which spreads through the v i s c e r a l c a v i t y surrounding the r a d u l a r sheath, esophagus, stomach and i n t e s t i n a l loops. I t com-122 F i g u r e 30. Diagram of a specimen o f C. p e l t a showing the ex t e n t o f the s a l i v a r y glands. The r e s t o f the v i s c e r a have been removed. The s a l i v a r y glands are s t i p p l e d . Maximum gland s i z e i s as drawn; minimum s i z e i s shown w i t h d o t t e d l i n e s . M a g n i f i c a t i o n approximately 8X. DSG, duct of the s a l i v a r y gland; LSG, l e f t s a l i v a r y gland; ME, midesophagus; PE, p o s t e r i o r esophagus; RG90, r e g i o n o f 90 degrees t o r s i o n o f the midgut; RSG, r i g h t s a l i v a r y gland; VC, v i s c e r a l c a v i t y . 123 DSG m RG90 RSG LSG PE VC 124 F i g u r e 31. Diagram of a specimen o f C. scutum showing the extent o f the s a l i v a r y glands. The r e s t o f the v i s c e r a have been removed. The s a l i v a r y glands are s t i p p l e d . Maximum gland s i z e i s as drawn; minimum s i z e i s shown w i t h d o t t e d l i n e s . M a g n i f i c a t i o n approximately 8X. DSG, duct of the s a l i v a r y gland; LSG, l e f t s a l i v a r y gland; ME, midesophagus; PE, p o s t e r i o r esophagus; RSG, r i g h t s a l i -v a ry gland; VC, v i s c e r a l c a v i t y . 125 126 F i g u r e 32. Diagram of a specimen of C. persona showing the e x t e n t o f the s a l i v a r y glands. The r e s t o f the v i s c e r a have been removed. The s a l i v a r y glands are s t i p p l e d . Maximum gland s i z e i s as drawn; minimum s i z e i s shown wit h d o t t e d l i n e s . M a g n i f i c a t i o n approximately 8X. DSG, duct of the s a l i v a r y gland; LSG, l e f t s a l i v a r y gland; ME midesophagus; PE, p o s t e r i o r esophagus; RSG, r i g h t s a l i v a r y gland; VC, v i s c e r a l c a v i t y . 127 DSG ME RSG LSG PE VC 128 municates wi t h the gut lumen by means of a duct which gi v e s o f f a branch to each of the two lobes of the gland. The lobes are not d i s t i n c t , the tubules o f each becoming c l o s e l y i n t e r m i n g l e d . Each branch o f the duct branches many times again i n t o a s e r i e s of d u c t u l e s which bear a l l along t h e i r l e n g t h many s m a l l e r , t e r m i n a l t u b u l e s . Both the d u c t u l e s and the t u b u l e s are of the same c e l l types, and are h i s t o l o g i c a l l y d i s t i n c t from the duct o f the d i g e s t i v e gland. D i f f e r e n c e s have been noted i n the morpho-logy o f -the d i g e s t i v e gland t u b u l e s i n the three C o l l i s e l l a s p e c i e s . In C. p e l t a the t u b u l e s are s h o r t and globose, approaching an a l v e o l a r or acinous shape. The m a j o r i t y of t u b u l e s are very n e a r l y as g r e a t i n width as they are i n l e n g t h . The t u b u l e s are never as long as the d u c t u l e s , and remain m o r p h o l o g i c a l l y d i s t i n c t from them as s m a l l t e r m i n a l bulbs ( F i g . 33a). L i t t l e i n d i -v i d u a l v a r i a t i o n i n t u b u l e shape was noted. F i g u r e 34 shows a p l a s t i c c a s t o f a p o r t i o n of the a n t e r i o r d i g e s t i v e t r a c t o f C. p e l t a , with the midesophagus, and p o r t i o n s o f the stomach and d i g e s t i v e gland t u b u l e s . In C- persona and C. scutum the t e r m i n a l tubules are much longer than i n C. p e l t a , b e i n g t u b u l a r i n shape ( F i g . 33b). The t u b u l e s are of 129 even diameter along t h e i r l e n g t h , and are o f t e n as long as the d u c t u l e s from which they a r i s e . For t h i s reason they are not always c l e a r l y d i s -t i n g u i s h a b l e from the d u c t u l e s . The tubules on the t e r m i n a l end of a d u c t u l e may be s h o r t e r i n le n g t h than the r e s t , but always the l e n g t h o f a s i n g l e tubule i s much g r e a t e r than the width. In C. persona l i t t l e i n d i v i d u a l v a r i a t i o n has been observed, the tub u l e s being c o n s i s t e n t l y t u b u l a r i n shape and always longer than those of C. p e l t a . I n d i v i d u a l v a r i a t i o n i s g r e a t e s t i n C. scutum. In t h i s s p e c i e s , while the tubules are t u b u l a r i n shape, they are much more v a r i a b l e i n t h e i r l e n g t h from i n d i v i d u a l t o i n d i v i d u a l . Some s p e c i -mens have t u b u l e s s i m i l a r i n l e n g t h t o those o f C. persona, y e t others possess tubules which are only h a l f as long. As i n C. persona, however, tubule l e n g t h i s g r e a t e r than t u b u l e width through-out most of the d i g e s t i v e gland. 130 F i g u r e 33. Diagrams o f p o r t i o n s o f the d i g e s t i v e gland showing the shape o f the t u b u l e s ; (a) C o l l i s e l l a p e l t a , (b) C o l l i s e l l a scutum and C o l l i s e l l a persona. DT, d u c t u l e s ; TB, t u b u l e s . 131 132 F i g u r e 34a. Photograph o f a p l a s t i c c a s t o f the a n t e r i o r d i g e s t i v e t r a c t o f C o l l i s e l l a p e l t a . F i g u r e 34b. Diagram of the above photograph. DFME, d o r s a l f o l d s o f the midesophagus; DGT, d i g e s t i v e gland t u b u l e s ; ME, midesophagus; S, stomach. 134 2. Histology of the Gut and Associated Glands General descriptions of the digestive t r a c t s of limpets belonging to the Acmaea complex have been made (Righi, 1966; Walker, 196 8; Fretter and Graham, 1962). Descriptions of general morphology of the t r a c t i n this study have, therefore, been avoided, and emphasis has been placed on characterization of the gut epithelium i n d i f f e r e n t parts of the system, and on the d i s t r i b u t i o n of mucocytes and other types of secretory c e l l s . No consistent differences i n gut histology were found between C o l l i s e l l a pelta, C. persona, and C. scutum. There were, however, d i s t i n c t l o c a l regions within the digestive t r a c t which could be distinguished by features of the gut epithelium. These features were consistent i n a l l specimens examined. The alimentary t r a c t can be divided into three main regions, the foregut, the midgut, and the hind-gut. The foregut includes the buccal cavity, the anterior esophagus, the midesophagus, and the poste-rior esophagus. The midgut consists of the proven^-t r i c u l u s , the stomach, and the i n t e s t i n e . The hind-gut includes the rectum and anus, i . The Foregut The mouth, v e n t r a l l y situated, i s oval i n outline and i s surrounded by a membranous f r i l l of outer l i p s . The mouth leads into a spacious 135 b u c c a l c a v i t y , with which there are a s s o c i a t e d many s t r u c t u r e s , i n c l u d i n g the i n n e r l i p s , the odontophore o r b u c c a l mass, the s u b r a d u l a r o r -gan, and the d o r s a l f o l d s . The e p i t h e l i u m of the b u c c a l c a v i t y i t s e l f v a r i e s i n appearance i n d i f f e r e n t p a r t s o f the c a v i t y . A n t e r i o r l y , and on the m i d l a t e r a l w a l l s throughout, the e p i t h e l i u m i s c u b o i d a l w i t h l a r g e n u c l e i which are c i r c u l a r i n o u t l i n e . I t i s approximately 12 to 15 micrometers i n h e i g h t . The n u c l e i do not s t a i n d a r k l y with haematoxylin. Two f o l d s , c a l l e d the d o r s a l f o l d s , pro-j e c t d o r s o - l a t e r a l l y i n t o the b u c c a l c a v i t y . These f o l d s p e r s i s t along the r o o f o f the c a v i t y p o s t e r i o r l y u n t i l the a n t e r i o r esophagus i s a t t a i n e d . As i n P a t e l l a , the f o l d s are composed of c o n n e c t i v e t i s s u e embedded w i t h numerous u n i -c e l l u l a r mucous glands. The gland c e l l s are A l c i a n b l u e p o s i t i v e and metachromatic w i t h T o l u i d i n e b l u e . The p o r t i o n o f the b u c c a l c a v i t y l o c a t e d between the p r o j e c t i n g f o l d s , the d o r s a l food channel, possesses a d i f f e r e n t type o f e p i t h e l i u m . Here the c e l l s are t a l l columnar, approximately 40 to 60 micrometers i n h e i g h t , w i t h c e n t r a l o r b a s a l e l l i p t i c a l n u c l e i . The c e l l s r e s t on a t h i n l a y e r o f muscle. Mucous c e l l s are o f t e n c l o s e l y asso-136 d a t e d a l s o w i t h the e p i t h e l i u m on the r o o f o f the d o r s a l food channel. The i n n e r l i p s hang down from t h e i r p o i n t o f attachment to the w a l l s o f the b u c c a l c a v i t y , p r o j e c t i n g i n t o the o r a l c a v i t y one on the l e f t and one on the r i g h t s i d e . T h e i r e p i t h e l i u m i s continuous with t h a t o f the b u c c a l c a v i t y . There are two d i f f e r e n t types o f e p i t h e l i u m c o v e r i n g each i n n e r l i p . That o f the proximal w a l l i s composed of a t a l l columnar e p i t h e l i u m ranging from 24 to 45 micrometers i n h e i g h t , with o v a l o r c i r c u l a r n u c l e i r e s t i n g on the bases o f the c e l l s . I n t e r n a l l y , and c l o s e l y a s s o c i a t e d with the proximal w a l l i s a band o f conn e c t i v e t i s s u e w i t h many embedded mucous gland c e l l s . Goblet c e l l s are found between the e p i t h e l i a l c e l l s near the d o r s a l l i m i t o f the proximal w a l l ( F i g . 35). Both the mucocytes and the g o b l e t c e l l s are f i l l e d w i t h l a r g e granules which are A l c i a n blue p o s i t i v e and metachromatic wi t h T o l u i d i n e b l u e . They s t a i n i n t e n s e l y w i t h D e l a f i e l d ' s haematoxylin. The d i s t a l w a l l o f each i n n e r l i p i s com-posed o f c u b o i d a l e p i t h e l i u m w i t h l a r g e s p h e r i c a l n u c l e i . The c e l l s range from 6 t o 15 micro-meters i n h e i g h t and are always one h a l f as t a l l (or l e s s ) than the c e l l s o f the proximal e p i t h e -lium. No gland c e l l s are a s s o c i a t e d with the e p i t h e l i u m i n t h i s r e g i o n . P o r t i o n s o f the ven-t r a l and d i s t a l w a l l s are covered w i t h a t h i n c u t i c l e . The outer l i p s are covered w i t h a very s h o r t columnar e p i t h e l i u m , 20 to 30 micrometers i n h e i g h t . The n u c l e i are c e n t r a l o r b a s a l i n p o s i -t i o n , c i r c u l a r i n o u t l i n e and possess prominent n u c l e o l i . The e p i t h e l i u m i s g r e a t l y f o l d e d on the v e n t r a l s u r f a c e and may, i n the a n t e r i o r r e g i o n s , be covered by a t h i c k c u t i c l e . The s u b r a d u l a r organ i s l o c a t e d v e n t r a l to the b u c c a l mass and between the two i n n e r l i p s . The e p i t h e l i u m o f t h i s s t r u c t u r e i s continuous with t h a t o f the i n n e r l i p s . I t i s protruded through the o r a l c a v i t y and p u l l e d over the sub-stratum w i t h each r a d u l a r p u l s a t i o n . The l a t e r a l e p i t h e l i u m i s c u b o i d a l d o r s a l l y . The c e l l s g r a d u a l l y i n c r e a s e i n h e i g h t towards the v e n t r a l end o f the w a l l s o f the organ, becoming s h o r t columnar, 12 to 30 micrometers i n h e i g h t , w i t h b a s a l s p h e r i c a l n u c l e i . I n t e r s p e r s e d between the e p i t h e l i a l c e l l s are g o b l e t c e l l s , s i m i l a r to those found w i t h i n the proximal e p i t h e l i u m o f the i n n e r l i p . Mucocytes are found c l o s e l y a s s o c i a t e d w i t h the basement membranes ..-of c e l l s i n t h i s r e g i o n . The v e n t r a l e p i t h e l i u m i s com-138 posed o f t a l l columnar c e l l s , 36 to 60 micro-meters i n h e i g h t . These c e l l s o f the v e n t r a l t i p o f the organ are always a t l e a s t twice as h i g h as those o f the l a t e r a l e p i t h e l i u m . The n u c l e i , which r e s t on the bases o f the c e l l s , are o v a l i n o u t l i n e and s t a i n l e s s i n t e n s e l y than do the c e l l s o f the l a t e r a l e p i t h e l i u m . The v e n t r a l regions o f the organ are covered by a t h i c k c u t i c l e . U n l i k e t h a t o f Acmaea subrugosa and A. marcusi ( R i g h i , 1966), there are no den-t i c l e s . The s u r f a c e of the s t r u c t u r e i s smooth. The s u b l i n g u a l c a v i t y i s an e x t e n s i o n o f the b u c c a l c a v i t y , l o c a t e d p o s t e r i o r to the o r a l tube and v e n t r a l to the b u c c a l mass. In c r o s s s e c t i o n i t appears as a s l i t , narrow i n h e i g h t but f a i r l y wide ( F i g . 36, SC). The d o r s a l e p i t h e l i u m o f the c a v i t y i s composed o f f l a t c u b o i d a l o r squamous c e l l s , 6 to 15 micrometers i n h e i g h t , w i t h c i r c u l a r or f l a t t e n e d n u c l e i which are n e a r l y one h a l f as t a l l as the c e l l s . These v e n t r a l c e l l s , approximately 30 to 48 micrometers i n h e i g h t , decrease suddenly i n l e n g t h a t the c o r n e r s of the c a v i t y . The ven-t r a l e p i t h e l i u m i s r a i s e d on e i t h e r c o r n e r o f the s l i t , and beneath these regions occur abun-dant u n i c e l l u l a r mucous glands embedded w i t h i n c o n n e c t i v e t i s s u e . Goblet c e l l s are found be-139 tween the e p i t h e l i a l c e l l s d o r s a l to the glandu-l a r areas ( F i g . 36). In the p o s t e r i o r regions o f the c a v i t y a few mucocytes are a l s o a s s o c i -ated with the d o r s a l e p i t h e l i u m a t the l a t e r a l edges o f the pouch. The e p i t h e l i u m becomes columnar i n the re g i o n s o f mucocyte a s s o c i a -t i o n . Both the g o b l e t c e l l s and the mucocytes c o n t a i n l a r g e granules which s t a i n densely with D e l a f i e l d ' s haematoxylin and are A l c i a n blue p o s i t i v e . The v e n t r a l e p i t h e l i u m i n the ce n t e r o f the s l i t i s covered by a t h i c k c u t i c l e ( F i g . 36). The b u c c a l mass (=odontophore) i s a l a r g e mass composed o f c a r t i l a g e s which are h e l d t o -gether and atta c h e d to the body w a l l by many p a i r s o f muscles. The c a r t i l a g e s (= b o l s t e r s ) are so named because h i s t o l o g i c a l l y they bear a g r e a t resemblance t o v e r t e b r a t e c a r t i l a g e ( F r e t t e r and Graham, 1962). The c e l l s o f the s t r u c t u r e are l a r g e and empty l o o k i n g w i t h very small c i r c u l a r n u c l e i u s u a l l y l o c a t e d a t the c e l l ' s p e r i p h e r y ( F i g . 36). The c e l l w a l l s and n u c l e i are metachromatic w i t h T o l u i d i n e b l u e . The muscles o f the b u c c a l mass occur i n t i g h t , densely packed bundles w i t h sma l l n u c l e i which are c i r c u l a r i n c r o s s s e c t i o n and elongate i n l o n g i t u d i n a l s e c t i o n . 140 The r a d u l a r sac runs along the s u r f a c e o f the b u c c a l mass i n a mid-dorsal groove. As i n P a t e l l a (Graham, 1932), a n t e r i o r l y i t i s as wide as the f o r e g u t , but narrows t o a tube of some-what s m a l l e r diameter. The t e e t h are atta c h e d to a r a d u l a r membrane (= i n f e r i o r e p i t h e l i u m o f the radula) which i s e o s i n o p h i l i c . D o r s a l l y , there i s a s u p e r i o r e p i t h e l i u m which i s c l o s e l y a s s o c i a t e d w i t h the d o r s a l s u r f a c e s o f the r a d u l a r t e e t h ( F i g . 37). The s u p e r i o r and i n -f e r i o r membranes are e n c l o s e d w i t h i n a sac, the e p i t h e l i u m o f which v a r i e s c o n s i d e r a b l y i n appearance. D o r s a l l y and d o r s o - l a t e r a l l y i t i s e i t h e r c u b o i d a l o r s h o r t columnar w i t h b a s a l c i r c u l a r o r o v a l n u c l e i . V e n t r a l l y the c e l l s compose a very t a l l columnar e p i t h e l i u m which s t a i n s densely w i t h haematoxylin. T h i s i s the r a d u l a r membrane ( F r e t t e r and Graham, 1962). The s u p e r i o r , i n f e r i o r and r a d u l a r membranes are a l l PAS p o s i t i v e , A l c i a n b l u e p o s i t i v e , and T o l u i d i n e blue p o s i t i v e (non-metachromatic). V e n t r a l to the r a d u l a r mem-brane there i s a t h i c k c u t i c l e which i s the subr a d u l a r (= e l a s t i c ) membrane ( F r e t t e r and Graham, 1962). In the a n t e r i o r r e g i o n s o f the r a d u l a r sac, near the d o r s a l w a l l s o f the narrow l a t e r a l e x t e n s i o n s , there are o c c a s i o n a l l y 141 F i g u r e 35a. Photograph o f a c r o s s s e c t i o n of the proximal i n n e r l i p e p i t h e l i u m o f C o l l i s e l l a p e l t a . Note the g o b l e t c e l l s (G) between the e p i t h e l i a l c e l l s , and the muco-cyt e s (MU) o f the i n t e r i o r o f the l i p . M a g n i f i c a t i o n 1000X. Haematoxylin and e o s i n . F i g u r e 35b. Diagram of the above c r o s s s e c t i o n . EIL, e p i t h e l i a l c e l l o f the proximal i n n e r l i p e p i t h e l i u m ; ESO, e p i t h e l i a l c e l l o f the s u b r a d u l a r organ; G, g o b l e t c e l l ; MU, mucocyte; N, nucleus. 143 F i g u r e 36a. Photograph o f a c r o s s s e c t i o n through the s u b l i n g u a l c a v i t y of C o l l i s e l l a p e l t a . Goblet c e l l s and mucocytes are l o c a t e d a t the extreme r i g h t and l e f t corners of the c a v i t y . M a g n i f i c a t i o n 266X. Haematoxylin and e o s i n . F i g u r e 36b. Diagram of the above c r o s s s e c t i o n . BG, b u c c a l g a n g l i o n ; CO, c a r t i l a g e of the odontophore; CU, c u t i c l e ; G, g o b l e t c e l l ; M, muscle; MO, muscle o f the odonto-phore; MU, mucocyte; SC, s u b l i n g u a l c a v i t y ; VE, v e n t r a l e p i t h e l i u m of the s u b l i n g u a l c a v i t y . 145 a few mucocytes associated with the bases of the e p i t h e l i a l c e l l s . The anterior esophagus i s characterized by the dorsal food channel, the l a t e r a l pouches and, p o s t e r i o r l y , by the development of two ven-t r a l folds, located on the f l o o r of the struc-ture. This portion of the gut i s more or less a continuation of the dorsal food channel of the buccal cavity, but has become i s o l a t e d from i t by the development of a septum which comes to form the f l o o r of the esophagus. The dorsal folds become somewhat reduced i n size i n compari-son with those i n the anterior buccal regions, due to the development of the l a t e r a l pouches which elaborate dorsally (Fig. 38). These folds are i d e n t i c a l h i s t o l o g i c a l l y to those of the buccal cavity, being composed of connective tissue and u n i c e l l u l a r mucous glands. The mucocytes are also concentrated along the roof of the dor-s a l food channel. The epithelium of the dorsal food channel i s c i l i a t e d , t a l l , columnar, 30 to 48 micrometers i n height, with basal, oval n u c l e i . The c i l i a are from 12 to 18 micrometers i n length. The ventral folds are located on the esophageal f l o o r , one to the r i g h t and one to the l e f t of the midline of the structure (Fig. 38). The folds are supported by connective tissue within 146 which are embedded mucocytes. Interspersed between the e p i t h e l i a l c e l l s of the ventral folds are often found goblet c e l l s . The muco-cytes of the dorsal and ventral folds and the goblet c e l l s of the ventral epithelium s t a i n strongly with Delafield's haematoxylin and are Alcian blue p o s i t i v e and metachromatic i n Toluidine blue. The c e l l s of the ventral folds, also c i l i a t e d , are very t a l l columnar, 36 to 66 micrometers i n height, with c e n t r a l , oval n u c l e i . The c i l i a range from 12 to 18 micro-meters i n length. The epithelium of the l a t - . eral pouches i s of a d i f f e r e n t type. The c e l l s are variable i n height and shape, ranging from cuboidal with large spherical nuclei to short columnar with oval n u c l e i . The columnar c e l l s are much shorter than those of the dorsal food channel and the ventral folds, and they are not c i l i a t e d . C e l l heights range from 12 to 42 mi-crometers. There are no mucocytes associated with the l a t e r a l pouches. Toward the posterior end of the anterior esophagus the walls of these pouches become extremely folded (Fig. 38). The ventral epithelium immediately beneath the dor-s a l food channel and between the ventral folds i s also of a t a l l c i l i a t e d columnar epithelium, s i m i l a r to that of the ventral folds and the d o r s a l food channel. A l l the c e l l s of the a n t e r i o r esophagus r e s t upon a t h i n l a y e r o f c onnective t i s s u e . The a n t e r i o r l i m i t of the midesophagus i s marked by the b e g i n n i n g of t o r s i o n . Here, the esophagus makes a gradual t w i s t to the l e f t through 180 degrees, as d e s c r i b e d by F r e t t e r and Graham (1962) and Graham (1932). The gut i n t h i s r e g i o n i s c h a r a c t e r i z e d by a g r e a t e l a b o r a t i o n of the l a t e r a l pouches, the w a l l s of which i n t e r n a l l y develop many rows of t r a n s v e r s e septa. The morphology o f these and the d o r s a l and v e n t r a l f o l d s o f the mid-esophagus i s as d e s c r i b e d f o r P a t e l l a (Graham, 19 32) and f o r Acmaea (= C o l l i s e l l a ) ( R i g h i , 1966). The l a t e r a l pouches e l a b o r a t e down around the v e n t r a l f o l d s , forming a narrow, s l i t - l i k e channel between the v e n t r a l e p i -t h e l i u m and the v e n t r o - l a t e r a l l i m i t s of the l a t e r a l pouches ( F i g . 39). The e p i t h e l i u m o f the d o r s a l food channel i s s i m i l a r to t h a t o f the a n t e r i o r esophagus, c o n s i s t i n g o f t a l l columnar c e l l s which are t h i c k l y c i l i a t e d . The b a s a l n u c l e i may be o v a l or elongate and possess prominent n u c e o l i . C e l l h e i g h t s range from 30 to 90 micrometers; c i l i a are from 15 to 40 micrometers i n l e n g t h . The d o r s a l f o l d s 148 F i g u r e 37a. Photograph of a s e c t i o n through the r a d u l a r sac o f C o l l i s e l l a persona. M a g n i f i c a t i o n 116X. Haematoxylin and e o s i n . F i g u r e 37b. Diagram of the above c r o s s s e c t i o n . AE, a n t e r i o r esophagus; CO, c a r t i l a g e of the odontophore; DSG, duct o f the s a l i v a r y gland; IER, i n f e r i o r e p i t h e l i u m o f the r a d u l a ; LN, l a b i a l nerve; LRS, lumen o f the r a d u l a r sac; MO, muscle of the odontophore; RM, r a d u l a r membrane; RT, r a d u l a r t o o t h ; SER, s u p e r i o r e p i t h e l i u m of the r a d u l a . 150 F i g u r e 38a. Photograph o f a c r o s s s e c t i o n through the a n t e r i o r esophagus o f C o l l i s e l l a scutum. M a g n i f i c a t i o n 2 00X. Haematoxylin and e o s i n . F i g u r e 38b. Diagram of the above c r o s s s e c t i o n . C, c i l i a ; DF, d o r s a l f o l d ; DFC, d o r s a l food channel; DSG, duct of the s a l i v a r y gland; LP, l a t e r a l pouch; MU, mucocyte; VF, v e n t r a l f o l d . 152 F i g u r e 39a. Photograph o f a c r o s s s e c t i o n through the midesophagus o f C o l l i s e l l a persona. M a g n i f i c a t i o n 97X. Haematoxylin and e o s i n . F i g u r e 39b. Diagram o f the above c r o s s s e c t i o n . DF, d o r s a l f o l d ; DFC, d o r s a l food channel; GD, gonad; LP, l a t e r a l pouch; ME, midesophagus; SG, s a l i v a r y gland; VF, v e n t r a l f o l d s . 154 have become reduced t o a p a i r o f long t h i n s t r e t c h -es o f conn e c t i v e t i s s u e accompanying the l a t e r a l w a l l s o f the d o r s a l food channel. Mucocytes occur w i t h i n the co n n e c t i v e t i s s u e of the f o l d s , s i t u -ated u s u a l l y a t the bases of the e p i t h e l i a l c e l l s . They empty t h e i r contents i n t o the lumen of the midesophagus v i a long t h i n necks which pass be-tween the e p i t h e l i a l c e l l s o f the d o r s a l food channel. Mucocytes are a l s o a s s o c i a t e d w i t h the connec t i v e t i s s u e c o v e r i n g the r o o f o f the d o r s a l food channel. A l l of these u n i c e l l u l a r mucous glands have prominent, c i r c u l a r , d a r k l y - s t a i n i n g n u c l e i and s i m i l a r s t a i n i n g p r o p e r t i e s to those mucous c e l l s a l r e a d y d e s c r i b e d . Small s e c r e t i o n d r o p l e t s which s t a i n densely with D e l a f i e l d ' s haematoxylin are seen among the c i l i a and i n the lumen o f the d o r s a l food channel, and are a s s o c i -ated• < w i t h the v e n t r a l f o l d s . As i n the a n t e r i o r esophagus, the e p i t h e l i u m of the v e n t r a l f o l d s i s composed of t a l l columnar c e l l s which possess t h i c k , l o n g c i l i a . C e l l h e i g h t s range from 36 to 66 micrometers and the c i l i a h e i g h t s from 12 to 18 micrometers. The o v a l or c i r c u l a r n u c l e i possess prominent n u c l e o l i , and u s u a l l y occupy a c e n t r a l p o s i t i o n w i t h i n the c e l l . The v e n t r a l f o l d s are supported by conn e c t i v e t i s s u e with embedded mucocytes o f the same type as those of 155 " the d o r s a l f o l d s . The l a t e r a l pouch e p i t h e l i u m a l s o resembles t h a t o f the a n t e r i o r esophagus. The c e l l s are s h o r t and of v a r i a b l e shapes rang-ing;? from s h o r t columnar to c u b o i d a l i n appearance. A l l the c e l l s have smal l c i r c u l a r , c e n t r a l n u c l e i with p a l e s t a i n i n g i n t e r i o r s and prominent, d a r k l y s t a i n i n g n u c l e o l i . Some c e l l s appear to have c i l i a , o t h e rs do not. A l l the c e l l s possess a f i n e l y g r a n u l a r cytoplasm, but d a r k l y s t a i n i n g s e c r e t i o n d r o p l e t s w i t h i n the cytoplasm, such as those r e p o r t e d i n P a t e l l a (Graham, 1932), were not observed. The esophageal glands (= p o s t e r i o r s a l i v a r y glands) are made up o f many l a m e l l a e which a r i s e from the w a l l s o f the l a t e r a l pouches. R i g h i (1966) d e s c r i b e s them as "fing e r - s h a p e d " . Each tubule i s l i n e d w i t h a s i n g l e l a y e r o f small c u b o i d a l c e l l s ( F i g . 40). These c e l l s possess long c i l i a which p r o j e c t i n t o the tubule lumen. Very s m a l l , d a r k l y s t a i n i n g s e c r e t o r y d r o p l e t s can o f t e n be seen among the c i l i a w i t h i n the lumen. The l i n i n g c e l l s ( c a l l e d " s e c r e t o r y " c e l l s by F r e t t e r and Graham, 1962) have l a r g e c i r c u l a r n u c l e i which s t a i n densely. The boundaries o f these c e l l s are not d i s c e r n i b l e . Surrounding the e p i t h e l i u m l i n i n g the tub u l e s i s a t h i c k l a y e r o f conne c t i v e t i s s u e , the n u c l e i 156 of which tend to be c o n c e n t r a t e d at the p e r i p h e r y of the t u b u l e s . They are a l s o dark s t a i n i n g and c i r c u l a r i n o u t l i n e . The c o n n e c t i v e t i s s u e l a y e r i s surrounded by a very t h i n sheet of muscle. The esophageal glands have been r e p o r t e d to s e c r e t e d i g e s t i v e enzymes ( F r e t t e r and Graham, 1962). Toward the p o s t e r i o r end o f the midesophagus the l a t e r a l pouches become s m a l l e r and the lumen narrows. The d o r s a l and v e n t r a l f o l d s g r a d u a l l y d i m i n i s h so t h a t there are l o n g i t u d i n a l f o l d s of equal magnitude a l l around the gut. T h i s marks the b e g i n n i n g of the p o s t e r i o r esophagus and the p o s t e r i o r l i m i t of t o r s i o n . T h i s p o r t i o n of the gut i s r e p o r t e d l y a simple tube c a r r y i n g food and enzymes to the stomach ( F r e t t e r and Graham, 1962). The e p i t h e l i u m i s composed of very t a l l columnar c e l l s , the h e i g h t s o f which are extremely v a r i a b l e . The c e l l s are u s u a l l y h i g h e s t a t the apex of a l o n g i t u d i n a l f o l d , becoming much s h o r t e r i n the v a l l e y s between the f o l d s ( F i g . 41). C e l l h e i g h t s a t the f o l d a p i c e s range from 75 to 135 micrometers. N u c l e i are b a s a l and u s u a l l y ex-tremely e l o n g a t e . The e p i t h e l i a l c e l l s possess s h o r t , but even and very dense c i l i a which are u s u a l l y 8 to 15 micrometers i n h e i g h t . The e p i t h e l i u m of the p o s t e r i o r esophagus i s thrown i n t o numerous w e l l - d e f i n e d l o n g i t u d i n a l f o l d s 157 which are supported by c o n n e c t i v e t i s s u e c o n t a i n -i n g embedded mucocytes. The mucocytes are con-c e n t r a t e d i n the r e g i o n s beneath the e p i t h e l i a l f o l d s and g e n e r a l l y near the bases o f the e p i t h e l i a l c e l l s . O c c a s i o n a l l y t h i n ducts may be seen p a s s i n g from the mucous gland c e l l s - be-tween the e p i t h e l i a l c e l l s to empty i n t o the lumen o f the esophagus. The gland c e l l s are PAS p o s i -t i v e , A l c i a n blue p o s i t i v e and T o l u i d i n e Blue p o s i t i v e (non-metachromatic). They sometimes s t a i n q u i t e f a i n t l y with haematoxylin. As i n most other regions of the gut, the p o s t e r i o r esophagus i s surrounded by a l a y e r of muscle f i b e r s , both c i r c u l a r and l o n g i t u d i n a l . i i . The Midgut The p r o v e n t r i c u l u s i s a s m a l l , expanded p o r t i o n of the gut s i t u a t e d between the p o s t e r i o r esophagus and the stomach. I t has been noted i n o t h e r s p e c i e s o f C o l l i s e l l a ( R i g h i , 1966; Walker, 1968) . As was d i s c u s s e d above, the placement of t h i s s t r u c t u r e d i f f e r s with r e s p e c t to the pos-t e r i o r esophagus and the stomach i n the three s p e c i e s ( C o l l i s e l l a p e l t a , C. persona, and C. scutum). In a l l three s p e c i e s the duct o f the d i g e s t i v e gland e n t e r s the gut a t the p o i n t o f 158 j u n c t i o n between the p r o v e n t r i c u l u s and the stomach. The a n t e r i o r w a l l s o f the p r o v e n t r i c u l u s are composed o f a columnar e p i t h e l i u m o f v a r i a b l e h e i g h t . The c e l l s are not thrown i n t o f o l d s , but r e s t . o n an even basement membrane u n d e r l a i n by c o n n e c t i v e t i s s u e and muscle l a y e r s . The c e l l s possess s h o r t , t h i c k , even c i l i a , approximately 12 to 15 micrometers i n h e i g h t , and b a s a l , o v a l or elongate n u c l e i . Approaching the p o i n t o f ent r y o f the p r o v e n t r i c u l u s i n t o . t h e stomach, the e p i t h e l i u m (on the w a l l o p p o s i t e to t h a t which the d i g e s t i v e gland duct enters) begins to change. The v a r i a b i l i t y i n the c e l l h e i g h t s g r e a t l y i n -creases so t h a t the appearance of f o l d i n g i s gi v e n , even though the basement membrane remains even. On the o t h e r w a l l , adjacent to the p o i n t o f e n t r y o f the duct o f the d i g e s t i v e gland, the e p i t h e l i u m o f both the p r o v e n t r i c u l u s and the stomach i s thrown i n t o a s e r i e s o f very t a l l l o n g i t u d i n a l f o l d s . The number o f f o l d s v a r i e s from animal to animal. T h i s r e g i o n may r e p r e s e n t a reduced p o s t e r i o r s o r t i n g area (Graham, 1949; R i g h i , 1966). From t h i s area o f f o l d e d e p i t h e l i u m run two f o l d s and a groove inbetween, which continue along the v e n t r o - l a t e r a l proximal w a l l o f the stomach. These are the two t y p h o l s o l e s w i t h the i n t e s t i n a l groove, as d e s c r i b e d f o r P a t e l l a (Graham, 19 32; 1949) and f o r Acmaea ( R i g h i , 1966). A s i m i l a r 159 arrangement, c a l l e d an "endostyle", has been d e s c r i b e d i n L o t t i a ( F i s c h e r , 1904). The stomach corresponds to "Region A" o f the gut o f P a t e l l a d e s c r i b e d by Graham (1932) and to "Region 1" o f C e l l a n a d e s c r i b e d by Rao (1975). As d i s c u s s e d above, the stomach and i n t e s t i n e f o l l o w a s e r i e s o f loops and c o i l s throughout the v i s c e r a l mass. As f o r L o t t i a ( F i s c h e r , 1904), the stomach l i e s i n one plane and completely en-c i r c l e s the v i s c e r a l mass near i t s perimeter. The lumen i s l a r g e , l a r g e r than i n any o t h e r p a r t of the midgut (as i n P a t e l l a and C e l l a n a ) . The stomach e p i t h e l i u m i s of c i l i a t e d columnar c e l l s o f v a r i a b l e h e i g h t s . Large groups of c e l l s o f even h e i g h t are separated u s u a l l y by three t o fo u r s h o r t e r c e l l s , thus g i v i n g the e p i t h e l i u m a waved appearance. The t a l l c e l l s are from 84 to 156 micrometers i n h e i g h t ; the s h o r t c e l l s v ary from 36 to 69 micrometers. The o v a l n u c l e i are b a s a l or c e n t r a l i n p o s i t i o n , o f t e n with prominent n u c l e o l i . C i l i a are s h o r t , even, and t h i c k , measuring approximately 9 to 15 micro-meters i n h e i g h t . The f a i r l y even basement mem-brane r e s t s on a very t h i n l a y e r o f t r a n s v e r s e muscle f i b e r s . No gland c e l l s were observed i n t h i s r e g i o n of the gut. The lumen of the stomach narrows as i t passes i n t o the i n t e s t i n e . There 1 6 0 i s no c l e a r c u t d i v i s i o n between the two. There are fo u r h i s t o l o g i c a l l y d i s t i n c t r e -gions w i t h i n the i n t e s t i n e . The boundaries of these regions are shown i n F i g u r e 42. The bound-ary l i n e s mark d i v i s i o n s made on the b a s i s o f the g r e a t e s t abundance of gland c e l l s . A few gland c e l l s c h a r a c t e r i s t i c o f a p a r t i c u l a r r e g i o n may p e r s i s t p a s t the boundary l i n e s o f the ad-j a c e n t r e g i o n s , but they are always very few i n number compared wit h t h e i r d e n s i t y i n the marked r e g i o n s . The fo u r regions are remarkably s i m i l a r h i s t o l o g i c a l l y to the corres p o n d i n g i n t e s t i n a l r e g i o n s d e s c r i b e d i n P a t e l l a (Graham, 19 32) and i n C e l l a n a (Rao, 1975) .-The e n t i r e i n t e s t i n e i s composed o f a t a l l columnar c i l i a t e d e p i t h e l i u m w i t h b a s a l o v a l n u c l e i , o f t e n with prominent n u c l e o l i . A s i n g l e l a y e r o f b a s a l granules can o f t e n be seen a t the bases o f the c i l i a , b l a c k a f t e r s t a i n i n g w i t h i r o n haematoxylin. The cytoplasm immediately below these i s o f t e n denser s t a i n i n g than t h a t o f the r e s t o f the c e l l . While some re g i o n s o f the i n -t e s t i n e are r e l a t i v e l y even i n c e l l h e i g h t , i n othe r regions the e p i t h e l i a l h e i g h t v a r i e s con-s i d e r a b l y . In these areas, a few extremely s h o r t c e l l s are separated by a group of t a l l e r c e l l s (as i n F i g . 43). These d i f f e r e n c e s i n c e l l h e i g h t s 161 probably r e p r e s e n t l o c a l i z e d ( i n t e r n a l ) l o n g i -t u d i n a l e p i t h e l i a l r i d g e s . The r e g i o n s i n which r i d g i n g o c c u r r e d were not found to be c o n s i s t e n t , but v a r i e d i n t h e i r l o c a t i o n from animal to animal. These r i d g e d areas may r e p r e s e n t p h y s i o -l o g i c a l l y a c t i v e r e g i o n s o f the gut. Regions i and i i are i d e n t i c a l h i s t o l o g i c a l l y , b e i n g comprised o f e p i t h e l i u m which i s smooth or v a r i a b l e i n h e i g h t with very s h o r t , even, dense c i l i a . C e l l s range i n h e i g h t from 24 to 100 micrometers; c i l i a are 2 to 12 micrometers i n l e n g t h . Region i i d i f f e r s from r e g i o n i i n t h a t the c i l i a are u s u a l l y s l i g h t l y l onger i n r e g i o n i i (from 12 to 15 micrometers) and i n t h a t the w a l l s are o f t e n , but not always, much more s t r o n g l y pigmented than the w a l l s of the r e s t o f the i n t e s t i n e . No gland c e l l s are p r e s e n t i n r e g i o n s i o r i i . Region i i i comprises a r e l a t i v e l y s h o r t l e n g t h o f the i n t e s t i n e , b e g i n n i n g where the pigmentation o f the p r e c e d i n g r e g i o n fades out. The e p i t h e l i u m i n t h i s r e g i o n i s s i m i l a r to t h a t of regions i and i i except f o r the presence o f a s m a l l gland c e l l , the b a s a l gland c e l l ( F i g . 43). The gland c e l l s which c h a r a c t e r i z e t h i s r e g i o n are s i m i l a r t o those named and d e s c r i b e d f o r P a t e l l a by Graham (1932). These s m a l l glands l i e between the bases o f the e p i t h e l i a l c e l l s , v a r y i n g 162 F i g u r e 40a. Photograph of a c r o s s s e c t i o n through the esophageal gland o f C o l l i s e l l a persona. Mag-n i f i c a t i o n 400X. Haematoxylin and e o s i n . F i g u r e 40b. Diagram o f the above c r o s s s e c t i o n . C, c i l i a ; CT, c o n n e c t i v e t i s s u e ; N, n u c l e i ; SC, s e c r e t o r y c e l l s . 164 F i g u r e 41a. Photograph o f a c r o s s s e c t i o n through the p o s t e r i o r esophagus o f C o l l i s e l l a persona. M a g n i f i c a t i o n 370X. Haematoxylin and e o s i n . F i g u r e 41b. Diagram of the above c r o s s s e c t i o n . C, c i l i a ; CT, con n e c t i v e t i s s u e , EPE, e p i t h e l i a l c e l l o f p o s t e r i o r esophagus; LPE, lumen o f the p o s t e r i o r esophagus; M, muscle; MU, mucocyte; N, n u c l e i . 166 F i g u r e 42. Diagram shov/ing the course of the i n t e s t i n e i n C o l l i s e l l a persona w i t h the f i v e h i s t o l o g i c a l r e g i o n s ( i - v ) . Boundaries of these regions are s i m i l a r l y l o c a t e d i n C o l l i s e l l a p e l t a and C o l l i s e l l a scutum. i , r e g i o n i ; i i , r e g i o n i i ; i i i , r e g i o n i i i ; i v , r e g i o n i v ; v, r e g i o n v; A, a n t e r i o r ; P, p o s t e r i o r ; R, rectum; S, stomach. 167 A iv v P 168 F i g u r e 43a. Photograph o f a c r o s s s e c t i o n through r e g i o n v o f the i n t e s t i n e of C o l l i s e l l a persona. Note the b a s a l gland c e l l s l o c a t e d between the bases o f the e p i t h e l i a l c e l l s . M a g n i f i c a t i o n 964X. Heidenhain's Iron Haematoxylin. F i g u r e 43b. Diagram o f the above c r o s s s e c t i o n . BGC, b a s a l gland c e l l ; CT, c o n n e c t i v e t i s s u e ; EC, e p i t h e l i a l c e l l s ; L I , lumen of the i n t e s t i n e ; M, muscle; NEC, n u c l e i of e p i t h e l i a l c e l l s . 170 i n s i z e and shape, but are most o f t e n one q u a r t e r the l e n g t h of the e p i t h e l i a l c e l l s or l e s s . They are u s u a l l y tear-drop shaped o r c i r c u l a r i n out-l i n e and they s t a i n b l a c k w i t h i r o n haematoxylin, and r e d w i t h haematoxylin and e o s i n . The c y t o -plasm appears to be densely packed wi t h f i n e g r a n u l e s . N u c l e i are s m a l l , c i r c u l a r i n o u t l i n e and c e n t r a l i n p o s i t i o n . The b a s a l gland c e l l s communicate wit h the lumen of the i n t e s t i n e by means of extremely long and t h i n ducts. I n t e s t i -n a l e p i t h e l i u m i n r e g i o n i i i ranges from 30 to 90 micrometers i n h e i g h t and the c i l i a from 6 to 18 micrometers. The average h e i g h t o f the b a s a l gland c e l l s i s 5 to 10 micrometers. The e p i t h e l i a l c e l l s of r e g i o n i v are s i m i -l a r to those d e s c r i b e d i n the p r e c e d i n g regions -t a l l columnar wi t h c i l i a o f moderate l e n g t h and b a s a l o v a l n u c l e i w i t h prominent n u c l e o l i . The r e g i o n i s c h a r a c t e r i z e d by the presence of two types of gland c e l l s . One of these i s the b a s a l gland c e l l , which i s the same as t h a t d e s c r i b e d i n the p r e c e d i n g r e g i o n . The o t h e r i s the c l a v a t e gland c e l l , s i m i l a r to t h a t d e s c r i b e d i n P a t e l l a (Graham, 1932) and i n C e l l a n a (Rao, .1975). These c e l l s , d e s c r i b e d by Graham as "club-shaped", were found i n most s e c t i o n s to be e i t h e r club-shaped, o r , more o f t e n , spindle-shaped ( F i g . 44). Located between the e p i t h e l i a l c e l l s , they r e s t on the basement membrane. U s u a l l y they are as t a l l as the e p i t h e l i a l c e l l s , b e i n g broadest a t the .prox-imal end, t a p e r i n g s l i g h t l y to form a long duct which d i s c h a r g e s i n t o the lumen of the i n t e s t i n e . The cytoplasm of the c l a v a t e glands i s packed wi t h l a r g e , d a r k l y s t a i n i n g granules which are l a r g e r and more conc e n t r a t e d near the base o f the c e l l ( F i g . 44). N u c l e i of the c l a v a t e glands are d i s t i n c t from the e p i t h e l i a l c e l l n u c l e i . B a s a l i n p o s i t i o n , the nucleus i t s e l f i s p a l e s t a i n i n g , but there i s a l a r g e dark s t a i n i n g n u c l e o l u s i n the c e n t e r . U n l i k e those r e p o r t e d f o r P a t e l l a (Graham, 1932), the granules o f the c l a v a t e glands s t a i n dark blue i n both Mayer's and D e l a f i e l d ' s haematoxylin. They are b l a c k a f t e r s t a i n i n g with i r o n haematoxylin and show a s t r o n g p o s i t i v e r e a c t i o n with T o l u i d i n e b l u e (no metachromasia). Reactions were ne g a t i v e w i t h both PAS and A l c i a n b l u e . The l a r g e s e c r e t i o n granules from the c l a v a t e gland c e l l s can o f t e n be seen i n the lumen of the i n t e s t i n e mixed wi t h food m a t e r i a l or a s s o c i a t e d w i t h the c i l i a o f the e p i t h e l i a l c e l l s . E p i t h e l i a l h e i g h t s i n r e g i o n i v range from 21 to 75 micrometers, t h a t o f the c l a v a t e glands from 23 to 4 7 micrometers (average h e i g h t ) , and the 172 c i l i a from 5 to 30 micrometers. Region v i s the l a s t r e g i o n o f the i n t e s t i n e . The e p i t h e l i a l c e l l s are s i m i l a r to those desr c r i b e d i n the pr e c e d i n g regions and may be even i n h e i g h t o r v a r i a b l e , forming l o c a l i z e d i n t e r n a l l o n g i t u d i n a l r i d g e s . The b a s a l gland c e l l i s the o n l y gland c e l l found i n t h i s s e c t i o n o f the gut and i t i s h i s t o l o g i c a l l y i d e n t i c a l with those of reg i o n s i i i and i v . The gland c e l l s are, however, much more abundant than i n the o t h e r two r e g i o n s . They become fewer i n number as the end o f r e g i o n v i s approached. C e l l h e i g h t s vary from 20 to 57 micrometers; c i l i a from 12 to 36 micrometers. i i i . The Hindgut The rectum begins a t the p o i n t where the i n t e s t i n e e n t e r s the mantle c a v i t y . I t c r o s s e s over from the l e f t o f the mantle c a v i t y to the r i g h t s i d e , suspended w i t h i n the o v e r l y i n g mantle along with the r i g h t r e n a l p a p i l l a . I t forms an a n a l p a p i l l a which i s f r e e a t i t s a n t e r i o r end. The w a l l s o f the rectum are thrown i n t o a number of l o n g i t u d i n a l f o l d s , two o f these f o l d s b e i n g much l a r g e r than the o t h e r s . T h i s g i v e s the lumen an S-shaped c o n f i g u r a t i o n ( F i g . 45). In a d d i t i o n , the w a l l s o f the two l a r g e s t f o l d s are themselves thrown i n t o a number o f s m a l l e r f o l d s a l l along .173 t h e i r l e n g t h . S i m i l a r arrangements are d e s c r i b e d f o r P a t e l l a (Graham, 1932) and f o r L o t t i a ( F i s c h e r , 1904). The f o l d s are l e s s marked i n the most "poste-r i o r p a r t o f the rectum, g r a d u a l l y i n c r e a s i n g i n h e i g h t and number u n t i l the t e r m i n a l anus i s reached. The e p i t h e l i u m i t s e l f i s of s h o r t colum-nar c e l l s with very long c i l i a . The c e l l s are approximately 15 to 30 micrometers i n h e i g h t w h i l e the c i l i a l e n g t h s range from 12 t o 36 micrometers. The b a s a l n u c l e i are c i r c u l a r o r o v a l i n o u t l i n e . E p i t h e l i a l c e l l s r e s t on a t h i c k l a y e r o f c o n n e c t i v e t i s s u e w i t h i n which are found abundant u n i c e l l u l a r mucous glands. These glands are of the same type as those found w i t h i n the f o l d s of the p o s t e r i o r esophagus, o f t e n s t a i n i n g p a l e b l u e w i t h D e l a f i e l d ' s haematoxylin. They show a l s o a p o s i t i v e r e a c t i o n w i t h A l c i a n b l u e . The c o n n e c t i v e t i s s u e o f the rectum i s surrounded by a t h i c k l a y e r of muscle, i v . The S a l i v a r y and D i g e s t i v e Glands The main mass o f tubules of the s a l i v a r y glands (= a n t e r i o r s a l i v a r y glands; b u c c a l glands), are l o c a t e d i n the a n t e r i o r and/or mid p o r t i o n s o f the v i s c e r a l mass. They empty i n t o the b u c c a l c a v i t y by a p a i r of l o n g ducts which pass a n t e r -i o r l y from the main mass on e i t h e r s i d e o f the esophagus. Being an acinous, e x o c r i n e compound 174 gland, i t i s composed of a compacted mass of many t u b u l e s . The duct r e p r e s e n t s one extremely long t u b u l e . In the main mass o f the gland, s m a l l amounts o f c o n n e c t i v e t i s s u e are found be-tween the s e c r e t o r y u n i t s . The ducts and the main mass o f tubules are h i s t o l o g i c a l l y i d e n t i c a l . The ducts are l i n e d with c u b o i d a l , c i l i a t e d c e l l s w ith c i r c u l a r n u c l e i . The c i l i a p r o j e c t i n t o the lumen, amongst which s e c r e t o r y d r o p l e t s can some-times be seen ( F i g . 46). These c e l l s are A l c i a n blue and PAS n e g a t i v e . Each t u b u l e , o r s e c r e t o r y u n i t , o f the gland i s composed o f a s i n g l e l a y e r o f c i l i a t e d c e l l s l i n i n g the lumen, and surrounding these a c l u s t e r o f s e c r e t o r y gland c e l l s , two to four c e l l l a y e r s deep. The s e c r e t o r y c e l l s are o f two types, as d i s t i n g u i s h e d by t h e i r s t a i n i n g p r o p e r t i e s . The f i r s t type, the alpha c e l l s , are of a very squat e p i t h e l i u m , c i r c u l a r o r o v a l i n o u t l i n e w i t h c i r c u l a r n u c l e i o f t e n l o c a t e d a t the c e l l p e r i p h e r i e s . The cytoplasm i s f i n e l y g r a n u l a r . The alpha c e l l s s t a i n p a l e pink with haematoxylin and e o s i n , and are p o s i t i v e i n A l c i a n b l u e , n e g a t i v e a f t e r PAS, and very weakly meta-chromatic with T o l u i d i n e b l u e . The second type o f c e l l , the beta c e l l s , are a l s o o f a squat e p i t h e l i u m but the cytoplasm i s f i l l e d w ith granules which s t a i n s t r o n g l y w i t h haematoxylin. 175 These c e l l s are PAS p o s i t i v e and A l c i a n blue n e g a t i v e . Two types of beta c e l l s can be d i s t i n -guished, one which s t a i n s densely, having c o a r s e l y g r a n u l a r cytoplasm, and one which s t a i n s l i g h t e r , having f i n e l y g r a n u l a r cytoplasm. The duct of the d i g e s t i v e gland i s l o c a t e d a t the p o i n t of j u n c t i o n o f the p r o v e n t r i c u l u s and the stomach, u s u a l l y a r i s i n g from the l e f t l a t e r a l w a l l or d o r s a l w a l l of the gut. As i n Acmaea (= C o l l i s e l l a ) subrugosa ( R i g h i , 1966) and P a t e l l a v u l g a t a (Graham, 1932), a s i n g l e duct a r i s e s from the gut w a l l which branches i n t o two, one branch e n t e r i n g each lobe of the d i g e s t i v e gland. The ducts are l i n e d with the same type o f t a l l columnar e p i t h e l i u m as t h a t o f the pro-v e n t r i c u l u s and the stomach, c h a r a c t e r i z e d by c e l l s of v a r i a b l e h e i g h t s , with s h o r t , even c i l i a and b a s a l o v a l o r elongate n u c l e i . The gland i t s e l f i s a very l a r g e t u b u l a r , compound gland which extends throughout almost the e n t i r e v i s -c e r a l c a v i t y , e n c l o s i n g the r a d u l a and i n t e s t i n e , and c o v e r i n g a p o r t i o n o f the stomach. The h i s -t o l o g y of the s t r u c t u r e i s s i m i l a r to t h a t o f P a t e l l a (Graham, 1932). The tubules are o f two types of c e l l s . The f i r s t type i s t h a t named by Graham (1932) the a b s o r p t i v e c e l l . These are t a l l columnar c i l i a t e d c e l l s w i t h b a s a l , c i r c u l a r n u c l e i 176 and f i n e l y g r a n u l a r cytoplasm ( F i g . 47). Prac-t i c a l l y every c e l l possesses one o r two l a r g e vacuoles a t the d i s t a l end which are f i l l e d w ith m a t e r i a l t h a t s t a i n s orange i n haematoxylin and e o s i n and i s A l c i a n b l u e p o s i t i v e . T h i s m a t e r i a l may r e p r e s e n t food which has been d i g e s t e d ex-t r a c e l l u l a r l y , c o n s o l i d a t e d i n mucous, and ab-sorbed by the a b s o r p t i v e c e l l s . Smaller and l e s s w e l l - d e f i n e d vacuoles occupy the cytoplasm imme-d i a t e l y below the l a r g e v a c u o l e s . U n l i k e those o f P a t e l l a , the n u c l e i possess a we 1.1 - d e f i n e d n u c l e o l u s . The a b s o r p t i v e c e l l s vary c o n s i d e r -a b l y i n h e i g h t from tubule to tubule and a l s o w i t h i n each tubul e (15 to 75 micrometers). The second type o f c e l l , the s e c r e t o r y c e l l s , are l e s s abundant i n the t u b u l e s than are the ab-s o r p t i v e c e l l s . As i n P a t e l l a (Graham, 1932) they occur e i t h e r s i n g l y or i n p a i r s s c a t t e r e d around the t u b u l e , o f t e n l y i n g a t the angles of the tubule w a l l s ( F i g . 47). They are most o f t e n t r i a n g u l a r i n o u t l i n e , being broader a t t h e i r bases. The nucleus l i e s i n the b a s a l h a l f of the c e l l . I t i s c i r c u l a r i n o u t l i n e and has a prominent n u c l e o l u s . The s e c r e t o r y c e l l s are f i l l e d w ith many l a r g e densely s t a i n i n g granules which are evenly d i s t r i b u t e d through the c y t o -plasm. The granules are dark blue with haema-t o x y l i n and e o s i n and show a s t r o n g (nonmeta-chromatic) s t a i n i n g r e a c t i o n w i t h T o l u i d i n e b l u e . The c e l l s are not c i l i a t e d and are of approximately the same h e i g h t range as the a b s o r p t i v e c e l l s . A l l the c e l l s o f the tubules r e s t on a t h i n l a y e r o f co n n e c t i v e t i s s u e , and between the tubules are found b l o o d spaces of the v i s c e r a l haemocoel w i t h i n which blood amoebocytes can o f t e n be seen. 178 F i g u r e 44a. Photograph of a c r o s s s e c t i o n through s e c t i o n i v o f the i n t e s t i n e of C o l l i s e l l a p e l t a . Note the c l a v a t e gland c e l l s between the e p i t h e l i a l c e l l s . M a g n i f i c a t i o n 14 00X. Heidenhain's Iron Haematoxylin. I F i g u r e 44b. Diagram of the above c r o s s s e c t i o n . CGC, c l a v a t e gland c e l l s ; EC, e p i t h e l i a l c e l l s ; L I , lumen of the i n t e s t i n e ; M, muscle; NCG, nucleus o f c l a v a t e gland c e l l . l&O F i g u r e 45a. Photograph of a c r o s s s e c t i o n through the rectum of C o l l i s e l l a scutum. M a g n i f i c a t i o n 335X. Haematoxylin and e o s i n . F i g u r e 45b. Diagram o f the above c r o s s s e c t i o n . C, c i l i a ; CT, connective t i s s u e ; DM, d o r s a l mantle; LF, l o n g i t u d i n a l f o l d s ; LR, lumen o f the rectum; M, muscle; MT, mantle t i s s u e . 182 F i g u r e 46a. Photograph o f a c r o s s s e c t i o n through a s a l i v a r y duct o f C o l l i s e l l a scutum. M a g n i f i c a -t i o n 590X. Haematoxylin and e o s i n . F i g u r e 46b. Diagram of the above c r o s s s e c t i o n . AC, alpha c e l l s ; BC, beta c e l l s ; C, c i l i a ; L, lumen of the duct; LC, c e l l s l i n i n g the duct; N, n u c l e i . 184 F i g u r e 47a. Photograph of a c r o s s s e c t i o n through the d i g e s t i v e gland t u b u l e s of C o l l i s e l l a persona. M a g n i f i c a t i o n 655X. Haematoxylin and e o s i n . F i g u r e 47b. Diagram of the above c r o s s s e c t i o n . AC, a b s o r p t i v e c e l l s ; C, c i l i a ; LT, lumen o f t u b u l e ; NAC, nucleus of a b s o r p t i v e c e l l ; SC, s e c r e t o r y c e l l ; V, vacuoles; VH, v i s c e r a l haemocoel. 186 F e c a l P e l l e t s Moore (19 31) i n h i s study on the morphology o f fe c e s of many s p e c i e s and genera o f B r i t i s h M o l l u s c a f o u n d s t h a t among the M o l l u s c a t h e r e e x i s t s a l a r g e range o f f e c a l shapes. He r e p o r t e d t h a t w h ile i n some genera the d i f f e r -ences i n shape o f any two s p e c i e s may be s u f f i c i e n t to p r o v i d e sound m o r p h o l o g i c a l c h a r a c t e r s f o r s p e c i e s d e t e r -mination, i n ot h e r genera there i s a gen e r a l p e l l e t type throughout the genus. Examination o f f r e s h l y shed p e l l e t s from many spec-imens o f C o l l i s e l l a p e l t a , C. persona, and C. scutum r e -v e a l e d no marked d i f f e r e n c e s i n morphology. In a l l three s p e c i e s the p e l l e t s take the form o f c y l i n d r i c a l rods, curved along t h e i r l e n g t h , and marked with a s i n g l e deep s p i r a l groove ( F i g s . 48a, 48b, and 48c). The p e l l e t s vary i n width from approximately 0.2 mm to 0.6 mm, t h i s measurement probably r e f l e c t i n g the s i z e o f the animal from which the p e l l e t was egested. Lengths o f the rods v a r i e d c o n s i d e r a b l y a l s o , r anging from approximately 1 mm to 10 mm. Since p e l l e t s are egested c o n t i n u o u s l y from the rectum suspended w i t h i n a mucous s t r a n d , the lengths o f the rods are no doubt determined by extraneous environmental f a c t o r s which a c t to break the p e l l e t s up (such as water c u r r e n t s ) . Although no m o r p h o l o g i c a l d i f f e r e n c e s i n the p e l l e t s were observed among the three s p e c i e s , c o n s i s t e n t d i f f e r -187 ences i n c o l o r a t i o n o f the feces were noted. In C. persona the p e l l e t s ranged from cream, brown, and green to b l a c k i n c o l o r . Most c o n t a i n e d v a r y i n g amounts of bl a c k p a r t i c u l a t e matter d i s t r i b u t e d evenly through the rods. Many of the f e c a l p e l l e t s were extremely dark i n c o l o u r due to the i n t e n s e c o n c e n t r a t i o n o f t h i s b l a c k p a r t i c u l a t e matter ( F i g . 48a). No l a r g e p i e c e s o f algae were ever observed w i t h i n , o r a s s o c i a t e d with, the mucous coat o f the p e l l e t s . The feces o f C.., scutum" were always of v a r i o u s shades of green, some w i t h y e l l o w i s h t i n g e s ( F i g . 48b). Extremely dark c o l o u r e d or b l a c k p e l l e t s , such as those c h a r a c t e r -i s t i c o f C. persona, were never observed i n t h i s s p e c i e s . In many of the p e l l e t s there were s m a l l e r amounts of very s m a l l brown p a r t i c u l a t e matter. A few of the p e l l e t s had some p i e c e s o f l a r g e m u l t i c e l l u l a r algae a s s o c i a t e d w i t h them. P e l l e t s egested by C. p e l t a ranged i n c o l o u r through shades of cream, yellow, g o l d , gray, l i g h t brown and dark brown. Many were s t r i p e d o r s p e c k l e d i n d i f f e r i n g shades of brown ( F i g . 48c). Very dark c o l o u r e d f e c e s , as are c h a r a c t e r i s t i c of C. persona, and g r e e n i s h c o l o u r e d f e c e s , as are produced by C. scutum, were never observed i n t h i s s p e c i e s . In a d d i t i o n , p i e c e s o f l a r g e m u l t i c e l l u l a r algae, i n c l u d i n g a filamentous type, were o f t e n compacted w i t h i n the feces o f C. p e l t a . 188 F i g u r e 48a. Photograph showing f e c a l p e l l e t s shed from C o l l i s e l l a persona. M a g n i f i c a t i o n approximately 13X. F i g u r e 4 8b. Photograph showing f e c a l p e l l e t s shed from C o l l i s e l l a scutum. M a g n i f i c a t i o n approximately 13X. 190 F i g u r e 48c. Photograph showing f e c a l p e l l e t s shed from C o l l i s e l l a p e l t a . M a g n i f i c a t i o n approximately 13X. IV. DISCUSSION A. F u n c t i o n a l Morphology T e s t (1945) suggests t h a t while some C o l l i s e l l a s p e c i e s are g e n e r a l i z e d f e e d e r s , u t i l i z i n g a v a r i e t y o f algae as food, o t h e r s p e c i e s demonstrate c o n s i d e r a b l e f e e d i n g s p e c i f i c i t y . T h i s has been shown f o r s e v e r a l spe-c i e s o f P a t e l l a (Branch, 1975). In h i s study i n A f r i c a n P a t e l l a , Branch found t h a t among some s p e c i e s a s p e c i f i c f o o d p l a n t i s e s t a b l i s h e d as a f e e d i n g t e r r i t o r y by the l i m -pet, and t h a t there i s a d i f f e r e n t i a t i o n o f food between a d u l t s and j u v e n i l e s . He a l s o observes t h a t o t h e r s p e c i e s are g e n e r a l i z e d browsers with no marked a d u l t - j u v e n i l e d i f f e r e n t i a t i o n w i t h r e s p e c t to food. Although no compar-abl e d e f i n i t i v e study on d i e t has been made f o r C o l l i s e l l a s p e c i e s , there i s g e n e r a l agreement i n the l i t e r a t u r e with r e s p e c t to the probable d i e t o f each of the s p e c i e s s t u d i e d . Both Test (1945) and Fritchman (1961b) s t a t e t h a t C. p e l t a appears to r e q u i r e macroscopic algae f o r food. Test (1945) r e p o r t s t h a t t h i s limpet s p e c i e s i s a very g e n e r a l i z e d feeder, capable o f u t i l i z i n g many d i f f e r e n t types of macroscopic algae and s e l e c t i n g C o s t a r i a , M a c r o c y s t i s , and P o s t e l s i a when a v a i l a b l e . N e i t h e r of these s t u d i e s r e p o r t s q u a n t i t a t i v e d a t a . C r a i g (1968) s t u d i e d food p l a n t s a v a i l -a ble i n fo u r r e g i o n s i n the i n t e r t i d a l zone, compared stom-ach contents o f C. p e l t a i n each of those r e g i o n s , and showed t h a t t h i s s p e c i e s i n g e s t s s i g n i f i c a n t l y g r e a t e r q u a n t i t i e s o f macroscopic algae than would be expected i f 193 f e e d i n g were n o n - s p e c i f i c . Both macroscopic and micro-s c o p i c algae are, however, pr e s e n t i n the d i e t o f t h i s s p e c i e s . I n d i v i d u a l s o f C. p e l t a which i n h a b i t the s t i p e s or h o l d f a s t s o f E g r e g i a have been a s s o c i a t e d w i t h s c a r s on the p l a n t , which are a p p a r e n t l y caused by e x t e n s i v e f e e d i n g ( C r a i g , 1968; P r o c t o r , 1968). The E g r e g i a form o f t h i s s p e c i e s , t h e r e f o r e , probably feeds upon the epidermal and c o r t i c a l c e l l s o f the p l a n t , as does C. i n s e s s a (Grant, 1937; McLean, 1966; P r o c t o r , 1968). C. i n s e s s a i s r e s t r i c t e d to the s t i p e and h o l d f a s t s o f E g r e g i a (Grant, 1937; Fritchman, 1961b; McLean, 1966). The animals feed upon the epidermal and c o r t i c a l c e l l s , p roducing deep s c a r s i n the p l a n t t i s s u e (Grant, 19 37; Fritchman, 1961b; P r o c t o r , 1968; Black, 1976). Test (1945, 1946) r e p o r t s t h a t C. scutum feeds upon the more d e l i c a t e v a r i e t i e s o f macroscopic algae, such as Ulva and Enteromorpha. Fritchman (1961a) con-s i d e r s t h a t t h i s s p e c i e s feeds p r i m a r i l y upon micro-s c o p i c a l g a l f i l m s , although some of the l a r g e r forms may a l s o be eaten. C. persona i s r e p o r t e d to scrape m i c r o s c o p i c algae o n l y ( T e s t , 1946; Fritchman, 1961a). Fritchman s t a t e s t h a t i n the m i c r o h a b i t a t o f t h i s s p e c i e s (high i n the i n t e r t i d a l zone) the o n l y p l a n t m a t e r i a l p r e s e n t i s u n i c e l l u l a r algae which grows along the bases o f the rocks and i n shaded c r e v i c e s . 194: While T e s t (1945) r e p o r t s t h a t C. l i m a t u l a scrapes d e l i c a t e macroscopic a l g a e , Fritchman (1961b) c o n s i d e r s t h i s s p e c i e s to be a " s c r a p e r o f bare rock s u r f a c e s " . In a study on gut contents and a v a i l a b l e foods o f C. l i m a t u l a , i t was found t h a t t h i s s p e c i e s s e l e c t e d p r i -m a r i l y e n c r u s t i n g red and c o r a l l i n e a lgae, i g n o r i n g the l a r g e r non-encrusting forms (Eaton, 1968). The above C o l l i s e l l a s p e c i e s may, t h e r e f o r e , be c l a s s i f i e d a c c o r d i n g to d i e t as f o l l o w s : 1. C o l l i s e l l a p e l t a - g e n e r a l i z e d feeder which scrapes both m i c r o s c o p i c and macroscopic algae, but which s e l e c t s f o r macro-s c o p i c forms (such as P e l v e t i a and Endocladia) 2. C o l l i s e l l a i n s e s s a - s p e c i f i c feeder which feeds o n l y upon E g r e g i a 3. C o l l i s e l l a scutum - g e n e r a l i z e d feeder which scrapes p r i m a r i l y m i c r o s c o p i c algae, but which may o c c a s i o n a l l y feed upon the more d e l i c a t e macroscopic forms (such as Ulva and E n t e r o - morpha) 4. C o l l i s e l l a persona - g e n e r a l i z e d feeder which scrapes m i c r o s c o p i c algae o n l y (the l o c a -t i o n o f t h i s s p e c i e s high i n the i n t e r t i d a l p r e c l u d e s the a v a i l a -b i l i t y o f l a r g e r forms) .195 5. C o l l i s e l l a l i m a t u l a - g e n e r a l i z e d feeder upon micro-s c o p i c ( e n c r u s t i n g red and c o r a l l i n e ) algae o n l y . The d i f f e r e n c e i n c o l o u r a t i o n o f the f e c a l p e l l e t s o f C. p e l t a , C. persona, and C. scutum found i n the p r e s -ent study suggests t h a t there i s a d i f f e r e n c e i n t h e i r d i e t s . I t was observed t h a t the stomachs o f i n d i v i d u a l s o f C. p e l t a o f t e n c o n t a i n e d l a r g e p a r t i c l e s and fragments of algae, and t h a t m u l t i c e l l u l a r a l g a l fragments and i n -t a c t filamentous algae were o f t e n observed i n the f e c a l m a t e r i a l . The stomachs o f C. scutum specimens o n l y r a r e l y c o n t a i n e d l a r g e fragments, c o n s i s t i n g mainly of very minute p a r t i c l e s . F e c a l m a t e r i a l o c c a s i o n a l l y had f r a g -ments of l a r g e algae a s s o c i a t e d with i t . In C. persona l a r g e a l g a l p a r t i c l e s were never observed i n the stomach o r f e c a l p e l l e t s . (No attempt was made i n the p r e s e n t study to i d e n t i f y stomach c o n t e n t s ) . T h i s evidence, however, would seem to support the above c l a s s i f i c a t i o n i n terms o f d i e t f o r these three s p e c i e s . McLean (1966) i n h i s taxonomic r e o r g a n i z a t i o n of the Acmaeidae suggests t h a t the s i z e and shape of the r a d u l a r t e e t h o f each s p e c i e s may be c o r r e l a t e d w i t h the food h a b i t s o f t h a t s p e c i e s . He observed t h a t "those s p e c i e s t h a t feed predominantly on c o r a l l i n e algae have s h o r t b l u n t t e e t h , those t h a t graze on m i c r o s c o p i c a l g a l f i l m s on the fronds of marine algae o r grasses have t e e t h w i t h broad s c r a p i n g edges, w h i l e those t h a t graze on rocks 196 i n t h e upper i n t e r t i d a l zone have l o n g t e e t h w i t h sharp c u s p s " (McLean, 1966). I n the p r e s e n t s t u d y a c o r r e l a -t i o n was noted between r a d u l a r t o o t h form and the s p e c i e s r e p o r t e d p r e f e r e n c e f o r e i t h e r m i c r o s c o p i c or macr o s c o p i c a l g a e (Table 3). In t h e s p e c i e s which s c r a p e s p r i m a r i l y m a c r o s c o p i c a l g a e (C. p e l t a ) , t h e r a d u l a r t e e t h demon-s t r a t e pronounced a n t e r i o r c u r v a t u r e and s h a r p l y p o i n t e d t i p s . The t e e t h o f C_. i n s e s s a , which a l s o s c r a p e s macro-s c o p i c a l g a e , a l s o have s h a r p l y p o i n t e d t i p s (McLean, 1966). In C. scutum, which s c r a p e s m i c r o s c o p i c and perhaps some m a c r o s c o p i c a l g a e , t h e r a d u l a r t e e t h a re o n l y s l i g h t l y r e c u r v e d and the t i p s a r e b l u n t . I n the s p e c i e s which r e p o r t e d l y f e e d upon m i c r o s c o p i c a l g a e o n l y (C. persona and C. l i m a t u l a ) , the r a d u l a r t e e t h show no c u r v a t u r e i a l o n g the cusp and the f l i p s a r e b l u n t and rounded. I t i s suggested t h a t t h e s e morpho-l o g i c a l d i f f e r e n c e s a re a d a p t a t i o n s which a l l o w t h e a n i -mals t o s c r a p e t h e i r r e s p e c t i v e p r e f e r r e d a l g a l forms w i t h g r e a t e r e f f i c i e n c y . The t e e t h of C. p e l t a , f o r example, may a c t upon t h e i r food as claws which a re c a p a b l e of t e a r i n g and b r e a k i n g o f f l a r g e chunks o f the p l a n t . The s h a r p l y p o i n t e d t i p s p a r t i c u l a r l y adapt the t e e t h f o r c u t t i n g . The b l u n t - t i p p e d , s t r a i g h t - c u s p e d t e e t h o f C. p e r s o n a and C. l i m a t u l a may a c t merely as r a k e r s o f t h e s u b s t r a t u m which Jkoosem p o r t i o n s o f a u n i c e l l u l a r a l g a l f i l m . The s m a l l e r p a r t i c l e s i z e o f 197 t h i s food type makes adaptations f o r c u t t i n g unnecessary. The t e e t h o f C. scutum c o u l d be c o n s i d e r e d as in t e r m e d i a t e i n form between the above two types. They may be adapted f o r s c r a p i n g u n i c e l l u l a r algae and d e l i c a t e macroscopic forms, but are perhaps i n c a p a b l e of c u t t i n g and t e a r i n g the tougher k e l p s as those of C. p e l t a are. I f the assumption i s made t h a t these C o l l i s e l l a s p e c i e s are adapted to a p a r t i c u l a r a l g a l d i e t , then evidence o f t h i s a d a p t a t i o n becomes apparent i n oth e r aspects o f the al i m e n t a r y system. These are summarized f o r C. p e l t a , C. persona, and C. scutum i n Table 3. C. l i m a t u l a i s a l s o i n c l u d e d i n the t a b l e , but r e p r e s e n t s data from three t o f i v e animals o n l y , which i n some cases were confirmed u s i n g diagrams from Walker (1968) and/or Grant (19 37). Most of the s t r u c t u r e s a s s o c i a t e d w i t h the d i g e s t i v e system e v i d e n c i n g m o r p h o l o g i c a l d i f f e r e n -t i a t i o n among the s p e c i e s are those r e l a t e d t o food a c q u i s i t i o n and i n g e s t i o n (namely, the r a d u l a r t e e t h and b a s a l p l a t e s , the jaw, and the s a l i v a r y g l a n d s ) . F u r t h e r , those s p e c i e s which r e p o r t e d l y scrape p r i m a r i l y micro-s c o p i c algae show the g r e a t e s t m o r p h o l o g i c a l s i m i l a r i t y i n the a l i m e n t a r y system. In these s p e c i e s , a l i m e n t a r y morphology i s d i s t i n c t from t h a t of C. p e l t a (Table 3). The b a s a l p l a t e s o f the r a d u l a d i f f e r among the sp e c i e s s t u d i e d i n the spacing o f ri b b o n u n i t s (Table 3). In C. p e l t a , the p l a t e s are c l o s e l y spaced w i t h some 198 Table 3: Summary of morphological characters of the alimentary system and t h e i r r e l a t i o n to reported d i e t . Scrapers of [ Scrapers of Macroscopic algaei Microscopic algae i Structure C. pelta C. scutum C. persona C. limatula Radular teeth anterior curvature great; t i p s sharply pointed s l i g h t anterior curvature; t i p s blunt but not rounded no curvature; t i p s blunt & rounded no curvature; t i p s blunt & rounded Spacing of basal plates c l o s e l y spaced; antero-posterior overlap c l o s e l y spaced but no overlap widely spaced widely spaced Anterior band of jaw prominent beak smooth or s l i g h t l y i r r e g u l a r smooth smooth Grooving of jaw deep grooves f a i n t grooves no grooving no grooving Size of s a l i v a r y glands very large small small small Diameter of stomach large small small small Position of proven-t r i c u l u s ventral side of stomach l e f t side of stomach anterior to stomach l e f t side of stomach Length of radular sheath short moderate long moderate to short Digestive gland tubules acinous tubular tubular mmm a-a — 199 degree o f a n t e r o - p o s t e r i o r o v e r l a p . Grant (1937) shows t h a t the p l a t e s o f C. i n s e s s a are a l s o c l o s e l y spaced wi t h marginal o v e r l a p . Both these s p e c i e s r e p o r t e d l y scrape macroscopic a l g a e . In the s p e c i e s which scrape m i c r o s c o p i c algae o n l y , the p l a t e s are wi d e l y spaced wi t h no o v e r l a p . In C. scutum, which may fe e d upon both m i c r o s c o p i c and macroscopic forms, the r i b b o n u n i t s are c l o s e l y spaced but there i s no o v e r l a p o f p l a t e mar-g i n s . T h i s d i f f e r e n c e i n b a s a l p l a t e s p a c i n g may be r e l a t e d to d i e t a r y a d a p t a t i o n . F l e x i b i l i t y o f the radu-l a r r i b b o n , f o r example, may be an important f a c t o r i n f e e d i n g . When f e e d i n g on a l a r g e , r i g i d k e l p s t i p e an i n f l e x i b l e r a d u l a r r i b b o n may be advantageous i n pro-v i d i n g s t a b i l i t y o f s t r o k e which i s needed f o r the c u t t i n g o f tough p l a n t t i s s u e . C l o s e l y spaced r i b b o n u n i t s might p r o v i d e t h i s i n f l e x i b i l i t y . C onversely, an animal which feeds p r i m a r i l y upon u n i c e l l u l a r a l g a l f i l m s may r e q u i r e a r a d u l a r ribbon with g r e a t e r f l e x i -b i l i t y i n o r d e r to f i t and bend with the i r r e g u l a r i t i e s o f the rock's s u r f a c e . Widely spaced b a s a l p l a t e u n i t s may provide a more f l e x i b l e r a d u l a r r i b b o n . The study o f b a s a l p l a t e s o f a d d i t i o n a l C o l l i s e l l a s p e c i e s i n con-j u n c t i o n with t h e i r f e e d i n g h a b i t s i s necessary f o r f u r t h e r e x p l o r a t i o n o f the s i g n i f i c a n c e o f b a s a l p l a t e spacing. The jaw i n P a t e l l a has been r e p o r t e d to f u n c t i o n i n the c o n t r o l o f the r a d u l a r t e e t h and b u c c a l mass 200 d u r i n g f e e d i n g (Graham, 1964). During odontophoral p r o t r a c t i o n and r e t r a c t i o n the moving r a d u l a i s h e l d f i r m l y a g a i n s t the v e n t r a l s u r f a c e o f the jaw. The move-ment of the r a d u l a upon the jaw produces the deep grooves which are found on the m i d - v e n t r a l s u r f a c e o f the jaw i n some C o l l i s e l l a s p e c i e s . Deep grooving has been r e p o r t e d i n the jaw o f P a t e l l a v u l g a t a (Runham and Thornton, 1967). These authors suggest two a d d i t i o n a l f u n c t i o n s o f the jaw due to the movement o f the r a d u l a r t e e t h along the jaw grooves: 1. to a i d i n the t r a n s p o r t o f detached food m a t e r i a l back i n t o the b u c c a l c a v i t y 2. to e f f e c t a r e d u c t i o n i n p a r t i c l e s i z e r e s u l t i n g from inward r o t a t i o n of the dominant t e e t h . The r o -t a t i o n may r e s u l t i n a s c i s s o r - l i k e c u t t i n g of the food. In the C o l l i s e l l a s p e c i e s s t u d i e d , grooving occurs o n l y i n those s p e c i e s which scrape macroscopic algae (Table 3). In C. p e l t a i t i s probable t h a t some inward r o t a t i o n o f the median and o u t e r l a t e r a l t e e t h takes p l a c e (as e v i -denced by grooving a n g l e s ) . Reduction o f p a r t i c l e s i z e due to a s c i s s o r - l i k e c u t t i n g o f algae caught upon the r a d u l a r t e e t h may, t h e r e f o r e , be a f u n c t i o n of grooving i n the jaw of C. p e l t a . I f the r a d u l a and jaw f u n c t i o n t o g e t h e r i n t h i s way, then i t seems reasonable t h a t grooving i s found o n l y i n those s p e c i e s which scrape macroscopic algae, s i n c e a d a p t a t i o n s which a c t to reduce 201 p a r t i c l e s i z e may be advantageous. In s p e c i e s which scrape u n i c e l l u l a r algae there i s no need to reduce p a r t i c l e s i z e . The s a l i v a r y glands i n most prosobranchs do not s e c r e t e d i g e s t i v e enzymes, but p r o v i d e l u b r i c a t i o n f o r the r a d u l a r apparatus d u r i n g f e e d i n g ( F r e t t e r and Graham, 1962). S t u d i e s made on limpets of other genera ( C e l l a n a  r a d i a t a , P a t e l l a v u l g a t a , F i s s u r e l l a barbadensis) i n d i -c a t e t h a t the s a l i v a r y glands l a c k d i g e s t i v e enzymes (Rao, 1975; Graham, 1932; Ward, 1966). Graham (1932) suggested t h a t s e c r e t i o n s produced from the glands may a l s o be i n -v o l v e d i n c o n s o l i d a t i o n and t r a n s p o r t of food p a r t i c l e s from the b u c c a l c a v i t y to the a n t e r i o r esophagus. In the s p e c i e s which scrapes l a r g e amounts of macroscopic algae (C. p e l t a ) the s a l i v a r y glands are much l a r g e r than i n those which scrape p r i m a r i l y m i c r o s c o p i c algae (Table 3). The r e l a t i v e s i z e of the s a l i v a r y glands i n C o l l i s e l l a s p e c i e s may r e f l e c t the amount of s e c r e t i o n r e q u i r e d . Perhaps the h a n d l i n g of l a r g e r p a r t i c l e s , such as have been t o r n from the f r o n d or s t i p e of a seaweed,requires a l a r g e volume of mucosubstance f o r c o n s o l i d a t i o n and t r a n s p o r t to the a n t e r i o r esophagus. Smaller p a r t i c l e s may r e q u i r e a s m a l l e r volume of s e c r e t i o n f o r c o n s o l i d a -t i o n . 202 H i s t o c h e m i c a l t e s t s i n d i c a t e t h a t the alpha c e l l s o f the s a l i v a r y glands produce a s i a l o m u c i n , and the beta c e l l s produce a n e u t r a l mucin (as i n d i c a t e d by t h e i r s t a i n i n g p r o p e r t i e s ) . The s a l i v a i s , t h e r e f o r e , a mucosubstance composed o f a mixture of these two s e c r e -t i o n s . Data on the l e n g t h o f the r a d u l a r sheath i n the f o u r s p e c i e s do not c l e a r l y f i t with the trends shown i n the o t h e r c h a r a c t e r s o f the d i g e s t i v e system, and may, t h e r e f o r e , not be r e l a t e d to d i e t (Table 3). The s i g n i -f i c a n c e of the d i f f e r e n c e s i n l e n g t h of the r a d u l a r sheath i s not c l e a r a t t h i s time. S t u d i e s made on p a t e l l i d l i mpets are i n g e n e r a l agreement t h a t i n t r a s p e c i f i c d i f f e r e n c e i n the l e n g t h o f the r a d u l a i s r e l a t e d to i n t e r t i d a l h e i g h t ( B r i a n and Owen, 1952; Rao and Ganapati, 196 7). I t has been suggested t h a t animals o f a s i n g l e s p e c i e s o c c u r r i n g h i g h i n the i n t e r t i d a l zone have lo n g e r radulae than those l o c a t e d i n lower i n t e r t i d a l r e g i o ns due to decreased f e e d i n g time, assuming t h a t the animals feed o n l y when submerged. The longer r a d u l a supposedly r e s u l t s from decreased use ( B r i a n and Owen, 1952; Rao and Ganapati, 1967). However, while limpets w i t h long radulae are u s u a l l y found h i g h i n the i n t e r t i d a l zone, there are some s p e c i e s occupying h i g h i n t e r t i d a l r e g i o ns which have s h o r t r a d u l a e . Koch (1949) found t h a t P a t e l l a v a r i a b i l i s occupying the h i g h i n t e r t i d a l shore has a s h o r t r a d u l a , while P. g r a n u l a r i s and P. oculus i n h a b i t i n g the same 203 zone have long r a d u l a e . In the C o l l i s e l l a s p e c i e s s t u d i e d here no simple c o r r e l a t i o n was found between r e l a t i v e r a d u l a r l e n g t h and i n t e r t i d a l h e i g h t . C. p e l t a , which i s found a t many i n t e r t i d a l l e v e l s from low to h i g h , has a s h o r t r a d u l a , c o n s t a n t i n l e n g t h over a l l i n t e r t i d a l l e v e l s . P o s s i b l y , there are other f a c t o r s a f f e c t i n g r a d u l a r l e n g t h among lim p e t s p e c i e s , such as the r a t e o f t o o t h s e c r e t i o n . A d i f f e r e n c e i n the morphology o f the d i g e s t i v e gland tubules was found between C. p e l t a (which are a l v e o l a r ) and C. scutum and C. persona (which are t u b u l a r ) . Although no h i s t o l o g i c a l d i f f e r e n c e o f the d i g e s t i v e gland t u b u l e s among these s p e c i e s was found, the m o r p h o l o g i c a l d i f f e r e n c e may be r e l a t e d t o f u n c t i o n . In some aspects o f the a l i m e n t a r y system no morpho-l o g i c a l d i f f e r e n c e was found among the three s p e c i e s . The p a t t e r n of mechanical wear shown by the r a d u l a r t e e t h w i t h i n the b u c c a l c a v i t y was s i m i l a r in. C. p e l t a , C. persona, and C. scutum. Since the wear on the r a d u l a r . t e e t h i s produced by t h e i r c o n t a c t with and movement over the substratum, the p a t t e r n o f wear r e f l e c t s the mode o f r a d u l a r m a n i p u l a t i o n d u r i n g f e e d i n g . The s i m i l a r i t i e s i n wear p a t t e r n s i n d i c a t e t h a t the r a d u l a i s moved over the substratum i n a s i m i l a r manner i n a l l three s p e c i e s . I t appears u n l i k e l y , t h e r e f o r e , t h a t the d i f f e r e n c e s i n r a d u l a r t o o t h form are r e l a t e d to a d i f f e r i n g mode o f m a n i p u l a t i o n o f the r a d u l a d u r i n g f e e d i n g . 204 No difference was found i n the histology of the gut epithelium or associated glands among the three species. The gut i s , i n fact, s i m i l a r anatomically and h i s t o l o g i -c a l l y to that of P a t e l l a (Graham, 1932), Cellana (Rao, 1975), and to other C o l l i s e l l a species (Righi, 1966). In a l l three genera the gut can be divided into three d i s t i n c t regions - the foregut, midgut and hindgut. Within each region the h i s t o l o g i c a l features (such as c i l i a t i o n and d i s t r i b u t i o n of mucus secreting and other gland c e l l s ) were s i m i l a r . The morphological s i m i l a r i t y i n gut anatomy and histology implies s i m i l a r i t y i n function. Once ingested, processing of food (digestion, absorption, production of fecal pellets) probably proceeds i n a simi-l a r manner, not only among C o l l i s e l l a species, but per-haps among the docoglossate limpets i n general. There i s a s i m i l a r trend i n many features of a l i -mentary morphology among those species which feed upon microscopic algae (C. scutum, C. persona, and C. limatula). The differences between these species and C. pelta (which scrapes large amounts of macroscopic algae) represent an apparent adaptation with respect to food preference. The concept of dietary adaptation becomes important when viewed i n the context of speciation by ecologic segrega-tion (Test, 1946). By thi s process species may ar i s e , not through geographical i s o l a t i o n , but through invasion of a previously unoccupied microhabitat, perhaps only a few feet away. The t r a n s i t i o n into the new microhabitat 205 may involve an alternate food source, such as that suggested for C. i n s t a b i l i s (Test, 1946). She suggests that, at some time when desirable foods were at a minimum, some variants of C. pelta which could tolerate Laminaria  andersonii as food and were able to withstand the greater time of submergence, invaded the vacant microhabitat upon thi s plant. Over time, t h i s variant population of C. pelta d i f f e r e n t i a t e d into what i s now recognized as C. i n s t a b i l i s . Previously u n u t i l i z e d food materials may, in t h i s way, be made available to the limpet population. Over time, the available food resources throughout the i n t e r t i d a l may eventually become partitioned among the inhabiting limpet species. Such a process acts to l i m i t i n t e r s p e c i f i c competition for food. Dietary adaptation, therefore, may have played an important role i n the successful exploitation of the i n t e r t i d a l environment by sympatric limpet species. B. Taxonomy The s h e l l , although s t i l l used extensively for i d e n t i f i c a t i o n , has been shown to be subject to extreme environmental v a r i a t i o n , and has, therefore, been consi-dered to provide unreliable c r i t e r i a for species deter-mination (Moore, 1934; Orton, 1933; Bonar, 1936; Curtiss, 1941; Test, 1946; McLean, 1966; Jobe, 1968). Greater emphasis has, therefore, been placed on the radular 206 teeth and basal plates as taxonomic characters, since they are not subject to environmental v a r i a t i o n (Grant, 1937; Curtiss, 1941; Fritchman, 1 9 6 0 b , ; McLean, 1966) . In the present study, additional characters of the radula, as well as some involving other structures of the alimentary system, are suggested as being useful for taxonomic pur-poses. They may be ranked from most r e l i a b l e to l e a s t r e l i a b l e (in terms of degree of v a r i a t i o n and ease of determination) as follows: 1. radular teeth arid basal plates 2. jaw shape and extent of grooving 3. length and configuration of the radula 4. position of the proventriculus 5. diameter of the stomach. Of a l l the characters investigated, the radular teeth were found to be the most r e l i a b l e i n terms of l i t t l e i n t r a s p e c i f i c v a r i a t i o n . No species overlap was observed, and the four species studied can be r e a d i l y distinguished on the basis of the features outlined i n the results ( i e . curvature of the median l a t e r a l s , sharp-ness of the t i p s , presence or absence of uncini, and degree of antero-posterior and/or l a t e r a l i n c l i n a t i o n ) . The unmounted basal plates display very l i t t l e i n t r a s p e c i f i c v a r i a t i o n . Distortion e f f e c t s are, however, produced by coverslipping the preparations. I f conven-t i o n a l l y mounted preparations are used for purposes of i d e n t i f i c a t i o n , t h e i r taxonomic value i s accordingly 207 reduced. T h i s problem can be avoided i f t h i c k mounts are used (as o u t l i n e d i n the m a t e r i a l s and methods). The shape of the a n t e r i o r band o f the jaw and the extent of grooving on the m i d - v e n t r a l s u r f a c e are a l s o s t a b l e c h a r a c t e r s i n the three s p e c i e s s t u d i e d . While they serve as c r i t e r i a f o r d i f f e r e n t i a t i o n o f C. p e l t a , C. persona,. and C. scutum, they may not prove adequate t o d i s t i n g u i s h o t h e r C o l l i s e l l a s p e c i e s . The l e n g t h and c o n f i g u r a t i o n o f the r a d u l a are suggested as good c h a r a c t e r s f o r d e t e r m i n a t i o n o f the thr e e s p e c i e s s t u d i e d . Although t h e r e i s a c e r t a i n amount o f v a r i a t i o n i n placement and s i z e o f loops, the g e n e r a l p a t t e r n i s i n v a r i a b l y the same i n C. p e l t a , and C. scutum. In C. persona v a r i a t i o n i n c o n f i g u r a t i o n i s somewhat g r e a t e r . Based on a sample of 60 animals, however, i t i s estimated t h a t r a d u l a r c o n f i g u r a t i o n alone can be used t o d i s t i n g u i s h a t l e a s t 94% o f a l l i n d i v i d u a l s o f the above three s p e c i e s . F u r t h e r , the c h a r a c t e r i s p a r t i c u l a r l y u s e f u l i n t h a t i n many cases s p e c i e s d e t e r m i n a t i o n merely i n v o l v e s o b s e r v a t i o n o f v i s i b l e p o r t i o n s o f the r a d u l a through the d o r s a l mantle a f t e r s h e l l removal. Again, while there i s no o v e r l a p among C. p e l t a , C. persona, and C. scutum, t h i s may not be the case among o t h e r s p e c i e s . The diameter of the stomach i s a c h a r a c t e r d i s t i n c t i n the three s p e c i e s s t u d i e d . While l i t t l e i n d i v i d u a l v a r i a t i o n i s d i s p l a y e d , assessment o f stomach s i z e 208 necessitates a subjective judgment on the part of the ob-server. Further, t h i s judgment becomes increasingly d i f f i -c u l t i f a l l three species are not available for compari-son, since the character has been documented comparatively for the three species. The looping of the intestine cannot be recommended as a means of species i d e n t i f i c a t i o n . While there are trends of difference among the three species, i n t r a s p e c i -f i c v a r i a t i o n i s great, contributing to considerable species overlap. Although considerable taxonomic problems have re-sulted among the acmaeid limpets from the use of the s h e l l for species i d e n t i f i c a t i o n , i t i s not suggested that the s h e l l be disregarded as a taxonomic t o o l . I t i s believed, rather, that no one character or structure should be r e l i e d upon so l e l y for species diagnosis. McLean (1966) based his r e v i s i o n of the Acmaeidae upon characters of both the s h e l l and the radular teeth. The use of the two characters i n combination provides a taxo-nomic scheme with greater u t i l i t y . As the morphology of these animals i s investigated more f u l l y , additional morphological characters w i l l be made available for taxonomic use. I t i s believed that the employment of these characters w i l l help to ease the problems of species i d e n t i f i c a t i o n presently, encountered among thi s group of animals. 209 V. SUMMARY Three s p e c i e s o f C o l l i s e l l a from Bowen I s l a n d , B r i t i s h Columbia were i n v e s t i g a t e d i n terms of s e l e c t e d aspects o f a l i m e n t a r y morphology. Char a c t e r s o f the r a d u l a were s t u d i e d u s i n g S.E.M. and l i g h t microscopy, i n c l u d i n g the t e e t h , b a s a l p l a t e s , l e n g t h , l o o p i n g and mechanical wear. The jaw and gut l o o p i n g were examined. H i s t o l o g y o f gut e p i t h e l i a and a s s o c i a t e d glands were i n v e s t i g a t e d . A i r d r y i n g produced d i s t o r t i o n s i n the s p a t i a l r e l a t i o n -s h i p s o f the r a d u l a r t e e t h , while c r i t i c a l p o i n t d r i e d radulae showed no evidence o f such d i s t o r t i o n s . A l i m e n t a r y morphology d i f f e r e d i n the three s p e c i e s i n the s p a t i a l r e l a t i o n s h i p s and form o f the r a d u l a r t e e t h , form and spa c i n g o f the b a s a l p l a t e s , l o o p i n g and r e l a -t i v e l e n g t h o f the r a d u l a r sheath, and s t r e n g t h o f jaw grooving and r e g u l a r i t y o f the a n t e r i o r band o f the jaw. D i f f e r e n c e s were a l s o noted i n l o o p i n g o f the i n t e s t i n e , s i z e o f the s a l i v a r y glands, p r o v e n t r i c u l u s placement, stomach diameter and shape o f the d i g e s t i v e gland t u b u l e s Wet weight o f s o f t p a r t s c h a r a c t e r i z e d more c l e a r l y the r e l a t i o n s h i p between r a d u l a r l e n g t h and animal s i z e than d i d s h e l l l e n g t h . Jaw grooving p a t t e r n s i n d i c a t e d t h a t some r o t a t i o n o f the median l a t e r a l s o f the r a d u l a upon the jaw may occur. Such r o t a t i o n may r e s u l t i n a r e d u c t i o n o f p a r t i c l e s i z e o f the food, as has been suggested i n P a t e l l a v u l g a t a . 210 6. The s a l i v a r y glands of C. p e l t a were much l a r g e r than have been p r e v i o u s l y r e p o r t e d i n t h i s s p e c i e s . 7. Mechanical wear p a t t e r n s of the r a d u l a r t e e t h d i d not d i f f e r i n the three s p e c i e s s t u d i e d . 8. H i s t o l o g y o f the gut and a s s o c i a t e d glands was s i m i l a r i n the three s p e c i e s . 9. Al i m e n t a r y morphology was c o n s i d e r e d i n terms o f each s p e c i e s r e p o r t e d d i e t . D i f f e r i n g m o r p h o l o g i c a l trends were found between the s p e c i e s which r e p o r t e d l y p r e f e r m i c r o s c o p i c algae and those which p r e f e r macroscopic algae. The s t r u c t u r e s were d i s c u s s e d w i t h r e s p e c t to the a d a p t a t i o n o f each s p e c i e s to i t s p r e f e r r e d a l g a l d i e t . 10. The s t r u c t u r e s which d i s t i n g u i s h the a l i m e n t a r y system i n the three s p e c i e s were c o n s i d e r e d with r e s p e c t t o t h e i r taxonomic v a l u e , and were ranked a c c o r d i n g to the degree of i n d i v i d u a l v a r i a t i o n found, and the ease o f det e r m i n a t i o n o f the c h a r a c t e r . The r a d u l a r t e e t h and b a s a l p l a t e s , jaw shape and ext e n t o f grooving, l e n g t h and c o n f i g u r a t i o n o f the r a d u l a , p o s i t i o n o f the proven-t r i c u l u s , and diameter o f the stomach a l l serve as r e l i -a b l e c r i t e r i a f o r de t e r m i n a t i o n o f the three s p e c i e s s t u d i e d . Gut l o o p i n g i s not recommended as a means o f d i s t i n g u i s h i n g these s p e c i e s due to c o n s i d e r a b l e i n d i v i -d ual v a r i a t i o n and s p e c i e s o v e r l a p . 211 LITERATURE CITED Anderson, T.F. 1951. 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