Abstract
The morphology and relation of a series of specialized structures, the expanded epipleural and associated muscle and nerves, Baudelot's ligament, and swim bladder, of Trachichthys australis, Optivus elongatus, Paratrachichthys trailli, and P.prosthemius are described.The shape and size of these structures vary according to species.Sexual dimorphism in these structures is seen in the two species of Paratrachichthys examined.The anatomical evidence suggests that these structures developed with a close relation of acoustic function.Based on the presence or absence of these structures, all known five genera in the family Trachichthyidae are divided into two phyletic stems, one comprising the present three genera and another comprising two genera, Hoplostethus and Gephyroberyx.
