1Abstract Evolution and Systematics of Holothuroidea (Echinodermata)

Holothuroids, or sea cucumbers, are a morphologically diverse group of echinoderms with over 1400 described species occurring from the intertidal to the deepest oceanic trenches. In this thesis, I investigate the evolution and systematics of this group via a phylogenetic analysis of partial nuclear small subunit rDNA sequences and morphological characters. The recovered cladistic structure of the group is identical between the data sets and is at considerable odds with the conventional higher level classification. The topology within at least one order, Apodida, is in contrast largely congruent with the Linnean scheme. Branching order is significantly associated with fossil first occurrences and the fossil calibrated tree indicates that holothuroids survived the end Permian extinction more successfully than other echinoderms. Like many other marine invertebrates, at least one clade radiated rapidly during the Triassic. Unlike echinoids, planktotrophic larvae are restricted to two evolutionarily disparate groups largely restricted to coral reefs