A morphological comparison of two closely related species of the genus Myoxocephalus (Pisces: Cottidae) with notes on their life histories and ecology.

Abstract

Two closely related and superficially similar species of the genus Myoxocephalus (M. polyacanthocephalus and M. jaok) were subjected to critical morphological comparison with the hope of determining features through which speciation and divergence may have operated. Also, but to a lesser extent their ecology and life histories were studied.It was found that although the two species are sympatric over much of their ranges, they differ (whether as adults or juveniles) in their depth distributions.Major differences were detected in their general color patterns, degree of sexual dimorphism, and squamation; also in the morphology of the cephalic lateral line system, and of the lateral line ossicles. Six meristic characters were examined, all but one being found to show significant differences between the two species. Meristic variation proved greater in M. polyacanthocephalus than in M. jaok.Twenty-three morphometric characters were measured and analyzed for the two species. From this it was demonstrated that the selected structures of the two species grew differently in relation to one another. In general M. polyacanthocephalus grew more rapidly than did M. jaok.In a number of instances, the dissimilarities appeared to reflect differences in ecological niches between the two species. Other differences appeared to be of most significance in terms of mate selection and species recognition.