The Pharyngeal Jaw Apparatus of the Embiotocidae (Teleostei): A Functional and Evolutionary Perspective

Abstract

Members of the Embiotocidae possess a single lower pharyngeal jaw suspended in either a single or double muscle sling. The single sling is formed by fusion of the levator externus 4 and central head of the obliquus posterior. Durophagous species have a second sling that is formed by fusion of the levator posterior with the lateral head of the obliquus posterior. During the highly stereotyped masticatory cycle both the lower and upper jaws undergo complex movement orbits resembling figure eights. During mastication the jaws execute shearing and crushing functions. Shearing occurs as the forward swinging upper jaws collide with the dorsally held lower jar. The time sequence in recruitment and duration of activity of the pharyngeal jaw muscles during the masticatory cycle show a constant pattern and are not influenced by prey size or type. The common pattern of ontogenetic differentiation of the muscle sling in the Embiotocidae, Cichlidae and Labridae has also produced a remarkable conservatism in the neuromuscular patterns underlying the masticatory cycles. The highly integrated pharyngeal jaw apparatus of Embiotocidae, Cichlidae and Labridae shares a common ontogenetic pattern and exhibits functionally as well as morphologically identical trends and striking parallelisms.