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Comparative morphology of selected aspects of the alimentary system of three species of limpets, Collisella pelta (Rathke), C. persona (Rathke) and C. scutum (Rathke) Latta, Lesley

Abstract

The morphology of the alimentary system was investigated in three species of Collisella, (C. pelta, C. persona, and C. scutum). The radular teeth were studied using the scanning electron microscope. The teeth of the above three species could be distinguished by the anterior curvature, anteroposterior and/or lateralinclination, sharpness of the tips, and presence or absence of uncini. Wear patterns of the radular teeth were similar in the three species. The radular basal plates could be differentiated by the anterior lobe, shape of the posterior margin, outline of the overlapping plates, and spacing of plates along the radular ribbon. Length and looping of the radular sheath was investigated. In C. persona the radular length (relative to body size) was greatest and the looping the most complex. In C. pelta the the radula was short and looping simple. C. scutum was intermediate in relative radular length and looping. Variation in radular looping was determined by a comparison of 60 individuals of each species from three different populations (20 of each species from three different localities). S.E.M. micrographs of the jaw showed that in C. pelta the anterior band bore a median tooth, and ventral grooving due to the radula was deep and distinct. In C. scutum the anterior band of the jaw was often irregular, and ventral grooving was faint. The jaws of C. persona had smooth anterior bands, and the ventral surface was unmarked. While looping of the intestine differed slightly among the three species, considerable individual variation and some species overlap was observed. Stomach diameter was larger in C. pelta than in the other two species. The placement of the proventriculus relative to the stomach and posterior esophagus differed in the three species. The salivary glands were much larger in C. pelta than in C. scutum and C. persona. Digestive gland tubules were acinous in C. pelta, but tubular in shape in C. scutum and C. persona. The histology of the gut epithelium and associated glands was studied using serial sections from 14 animals. No differences among the three species were found. Morphology of the above structures was considered with respect to the reported diet of each species. A correlation was found between radular tooth form and the species reported preference for either microscopic algae or macroscopic algae. The correlation was considered to be indicative of dietary adaptation. The morphology of the radular teeth and the other characters studied (basal plates, jaw, salivary glands) were discussed with respect to the adaptation of each species to its preferred algal diet. The characters investigated were considered with respect to their taxonomic value. They were ranked according to the degree of individual variation found, and ease of determination of the character.

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