A classification and phylogeny of post-Palaeozoic sea stars (Asteroidea: Echinodermata)

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Abstract
A revised classification and phylogeny at the family level and above are presented for post-Palaeozoic sea stars. Monophyly of the group is established by a character suite taken from the ambulacral column that thus far has been recognized in only one Palaeozoic genus. Compared to earlier studies, character selection here placed relatively greater emphasis on morphology and arrangement of ossicles and ossicular systems. Functional implications of many features are surveyed. Thirty-four families, three extinct, are recognized and a number of older familial concepts are suppressed; the extinct Trichasteropsidae is proposed. Superfamilies are recognized for the Valvatida. Eight orders, including the new, extinct Trichasteropsida, and three superorders are recognized. No living sea star is primitive in the sense of being close to ancestral sea stars and other echinoderm groups; the Paxillosida, which commonly has been considered primitive, is here considered specialized.