Morphology and Function of Pectoral Fin Muscles in Lizardfishes (Actinopterygii: Aulopiformes: Synodontidae), with Comments on an Additional Muscle of the Fin

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The morphology of the pectoral fin muscles of lizardfishes (Synodontidae) is described. Members of this family commonly have six pectoral fin muscles: the abductor superficialis, abductor profundus, arrector ventralis, adductor superficialis, adductor profundus, and arrector dorsalis. An additional muscle, the arrector medialis (named in this study), was discovered on the mesial side of the pectoral fin in all nine examined species of Synodus and Trachinocephalus, but is absent in all four examined species of Harpadon and Saurida. It inserts on an anterior process of the base of the mesial half of the uppermost ray and appears to have a function similar to that of the arrector ventralis in supporting the protraction of the uppermost ray and the abduction of the pectoral fin. This muscle supports the division of the synodontids into two groups (present in Synodus and Trachinocephalus vs absent in Harpadon and Saurida). The function of the arrector medialis is morphologically discussed.