Diversity and evolution of larval patterns in holothuroid echinoderms

MINER, B.G*; MCEDWARD, L.R.: Diversity and evolution of larval patterns in holothuroid echinoderms

Larval types and developmental patterns have been well studied in the echinoderm classes, asteroids and echinoids. In contrast, the other classes of echinoderms, crinoids, holothuroids, and ophiuroids, have been ignored. We have reviewed the literature on 69 species of holothuroids focusing on the phylogenetic distribution of developmental patterns and larval types within the clade. There are three observed larval types: auricularia, doliolaria, and vitellaria. Although not documented, facultative planktotrophy and a direct development may exist. Phylogenetic distribution of these larval types suggests that the auricularia has been lost 8 times, and that the vitellaria has evolved 3-6 times within the group. The developmental patterns that have been documented are planktotrophy, pelagic lecithotrophy, and benthic lecithotrophy. Assuming a planktotrophic ancestor, the phylogenetic distribution of these patterns suggests that brooding has evolved 6 times within the holothuroids. In light of the few studies documenting developmental types within holothuroids, the possible evolutionary changes that can explain the observed types are complex. Future studies on developmental diversity, as well as a better understanding of phylogenetic relationships, are necessary to elucidate the evolution of larval patterns in this group.

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