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Comparative morphology of two closely related species of the Cottid genus Myoxocephalus Cowan, Garry I. McT.

Abstract

A detailed morphological study has been made between two apparently closely related species of the cottid genus Myoxocephalus (Steller) Tilesius, Myoxocephalus polyacanthocephalus Pallas and Myoxocephalus jaok (Cuvier and Valenciennes), Large series of both species were examined. Coloration was found to be one of the major differences, between the two species. They were also found to differ in the degree of sexual dimorphism. Sguamation, the lateral line system, and osteology were examined by clearing and staining. The scales and lateral line ossicles were found to be morphologically distinct. The osteology was essentially similar in both species, the only major difference being the loss of the third preopercular spine in M. jaok. The musculature of head and caudal regions was examined in detail but no significant differences were encountered. A preliminary examination of the 1 muscle proteins by means of starch-gel electrophoresis was also undertaken. Distinct differences in the mobilities of several protein bands were encountered. Analyses of meristic characters revealed large variation, and almost complete range overlap between the two species. The modes of several of these counts however, were different. Morphometric characters indicated close similarity and of the 32 measurements taken and the 992 combinations compared, only two yielded significant differences„ These were depth of caudal peduncle against length of anal fin base and depth of caudal peduncle against length of second dorsal fin base.

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