Cladistic methods are used to investigate phylogenetic relationships of the Indo-Pacific marine fish family Plesiopidae. Using multiple outgroups, osteological and myological characters indicate that plesiopids are monophyletic only with the inclusion of the Acanthoclinidae as the sister
group to the genus Plesiops. A new classification lowers the Acanthoclinidae to subfamilial rank, and other monophyletic units are recognized at this same rank to produce the following phylogenctically sequenced classification (included genera in parentheses): Trachinopinae (Trachinops),
Assessorinae (Assessor), Paraplesiopinae (Paraplesiops, Calloplesiops, Steeneichthys), Fraudellinae (Fraudella), Plesiopinae (Plesiops), Acanthoclininae (Acanthaclinus, Belaneplerygian, Behaps, Acanthoplesiops). This phylogeny suggests that egg mass guarding
is plesiomorphic for the family, and that oral incubation in Assessor is autapomorphic. A diagnosis for the newly defined family is provided.
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