Morphology of the parrotfish pharyngeal jaw apparatus

Abstract

SYNOPSIS. Analysis of the anatomy of the pharyngeal apparatus of parrotfish demonstrates extraordinary specialization of the grinding jaws. The epibranchials have lost their gill-bearing function. The first epibranchial is the structural element of the pharyngeal valve that is operated by the first levator externus, first branchial adductor and part one of the transversus dorsalis muscles. Five pairs of muscles (fourth levator externus, levator posterior lateralis and medialis, fifth branchial adductor, part two of the transversus ventralis) are positioned to adduct the lower pharyngeal. The retractor dorsalis and fourth obliquus dorsalis are positioned to retract the upper pharyngeal. The third levator internus and transversus dorsalis posterior protract the upper pharyngeal. The fourth levator externus, both parts of the levator posterior and the fifth adductor are massive and pinnate. Deep fossae for the attachment of the fourth levator externus and levator posterior muscles are sculpted out of the neurocranium. A ventral spike process of the prootic and expanded hemal postzygapophyses of the first three vertebrae are skeletal features associated with the elaborated musculature of the pharynx. Synovial joints are present between the basicranium and upper pharyngeals, between the upper pharyngeals and fourth epibranchials and between the lower pharyngeal and cleithrum. The upper pharyngeals act as a single unit bound by cruciate ligaments. The fourth epibranchial is a key element in the pharyngeal apparatus and serves to direct forces generated by the transversus ventralis, fifth adductor, levator posterior lateralis, transversus dorsalis posterior and fourth obliquus dorsalis. © 1989 by the American Society of Zoologists.