The gill-arch musculature and associated aspects of the skeleton of the anguilliforms Protanguilla, Conger, Anguilla, and the synaphobranchids Synaphobranchus and Simenchelys are described, illustrated, and compared. We identify nine anguilliform synapomorphies, seven myological and two osteological and all but two reported for the first time. We also describe one myological and one osteological synapomorphy of the Anguilliformes minus Protanguilla. Our study strongly corroborates the monophyly of the Anguilliformes, which has never been seriously challenged by morphological evidence, and is also supported by molecular analyses. Furthermore, it offers additional morphological support for placing Protanguilla as the sister group of all other eels. The condition of many gill-arch skeletal and muscular features are also treated in other elopomorphs and, occasionally, osteoglossomorphs and more primitive actinopterygians. For comparison, we also include the description of the gill-arch muscles of a specialized eel species of the family Serrivomeridae and discuss analyses of its closest family relationships as indicated by several molecular studies.

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