Comparative study of the cranial morphology of the labrids Choeroden venustus and Labroides dimidiatus and the scarid Scarus fasciatus (Pisces : Perciformes) I. Head skeleton

Abstract

The cranial osteology of C. venustus, L. dimidiatus and S. fasciatus is described. C. venustus and L. dimidiatus possess three features characteristic of the family Labridae: protrusible upper jaws, the ascending process of the maxilla longer than the alveolar process, and the alveolar process of the premaxilla attached by fibrous tissue to the distal end of the maxilla which in turn is fastened to the ascending process of the dentary. The neurocranium of C. venustus shows several features involved in strengthening the skull to withstand the strong forces applied during feeding when crushing molluscs, barnacles and crabs as well as turning over slabs of coral. The forward movement of jaws and eyes have permitted L. dimidiatus to feed by picking small organisms off the general body surface, pharynx, gills and buccal cavity of host fish. S.fasciatus has at least three features characteristic of scarids: fused teeth on the premaxillae and dentary, a premaxilla firmly attached to the maxilla, and a secondary joint between the dentary and articular producing a compound lever type of articulation for the lower jaw. Several modifications help strengthen the upper and lower jaws and enable S. fasciatus to feed by scraping pieces of algae and coral fragments from the surfaces of coral rocks.