Comparative study of the cranial morphology of the labrids Choeroden venustus and Labroides dimidiatus and the scarid Scarus fasciatus (Pisces : Perciformes) II. Cranial myology and feeding mechanisms

Abstract

Detailed descriptions of the muscles involved in the jaw movements in C. venustus, L. dimidiatus and S. fasciatus are presented. The function of individual muscles and their importance in jaw movements during feeding are suggested from interpretation of dissections and observations of feeding behaviour recorded in the literature. The extreme development of epaxial musculature in C. venustus and S. fasciatus braces the head during feeding when large forces are applied to the lowerjaw by C. venustus in removing barnacles from rocks and overturning slabs of coral and by S.fasciatus in scraping bits of algae from coral rocks. The lack of a protrusible upper jaw in S. fasciatus results from several features: loss of the twisting movement of the maxillary head found in C. venustus and L. dimidiatus. the development of a secondary articulatory joint about the articular, loss of attachment of A₁ to the premaxillary condyle of the maxillary head, and a decrease in the size of the lateral process of the premaxilla when compared to that found in C. venustus and L. dimidiatus. The well-developed levator arcus palatini muscle probably permits the development of a powerful suction important in the capture of prey organisms in L. dimidiatus. The large hypobasihyal bone in L. dimidiatus may help to control the movement of prey through the buccal cavity. Its distinctive bilobed lower lip may enhance the powerful suction in the buccal cavity and be useful during feeding when the caniform teeth are not engaged in prey capture.