Phylogeny of Holothuroidea (Echinodermata) inferred from morphology

Holothuroids, or sea cucumbers, are an abundant and diverse group of echino derms with over 1400 species occurring from the intertidal to the deepest o ceanic trenches. In this study, we report the first phylogeny of this class , based on a cladistic analysis of 47 morphological characters. We introduc e several previously unconsidered synapomorphic characters, examine the rel ationships between representatives from all extant families and assess the assumptions of monophyly for each order and subclass. Maximum-parsimony ana lyses using three rooting methods recovered well-supported and identical to pologies when two small and apparently derived families, Eupyrgidae and Gep hyrothuriidae, were removed. The results suggest that the higher-level arra ngement of Holothuroidea warrants a considerable revision. Apodida was sist er to the other holothuroids. The monophyly of Dendrochirotida was not supp orted and the group may be paraphyletic. A randomization test using Wills' gap excess ratio found significant congruence between the phylogeny and the stratigraphic record of fossil members, suggesting that the fossil record of holothuroids is not as incomplete as is often stated. The fossil-calibra ted tree indicated that several groups of holothuroids survived the end-Per mian mass extinction and that the clade composed of Dendrochirotida, Dactyl ochirotida, Aspidochirotida and Molpadiida rapidly radiated during the Tria ssic. (C) 2001 The Linnean Society of London.