PHARYNGEAL JAW STRUCTURE IN LABRID FISH

Abstract

The structure of the pharyngeal jaw in labrid fishes was examined. Materials examined as for the fourth levator extern us, levator posterior and postpharyngeal ligament included 21 genera and 44 species. Relationships between degree of development of the pharyngeal jaw structure and feeding habit were discussed. These fishes were classified into seven types based on the structural pattern of levator posterior with existence of the supraoccipital crest in mind. The results obtained are shown as follows: I) The fourth levator externus and levator posterior insert mainly on the lower pharyngeal bone and show a tendency to the independence of it as a feeding structure. 2) On the whole, the pharyngeal jaw structure is well-developed in hard-biting species which feed mainly on tough preys like molluscs and echinoids. 3) Each type of the levator posterior clearly corresponds to the feeding habit. The levator posterior plays an important role in feeding. 4) In Type PA, the supraoccipital crest serves as a site of insertion for the levator posterior. It also functions as a site of insertion for only the epaxial muscle in generalized percoid fishes and seems to be related to the body depth. 5) Mechanical differentiation of types was speculated.