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Janies, Daniel A. Department of Bioinformatics and Genomics, University of North Carolina, Charlotte, North Carolina.
- Echinoderm design
- Phylogeny of echinoderms
- Genetic and developmental studies of Xyloplax
- Life-cycle adaptations
- Related Primary Literature
- Additional Reading
The echinoderms include familiar marine organisms such as sea stars and sea urchins, as well as other extant forms such as sea lilies (crinoids), sea cucumbers, and brittle stars. Lineages of these forms represent the five living classes of echinoderms. The notion of only five classes was recently challenged by the discovery of Xyloplax (Fig. 1). Xyloplax is a genus of small, disk-shaped echinoderms that were first discovered in 1984 based on specimens collected from sunken wood recovered from depths of 1100 m (3600 ft) off New Zealand. Other species of Xyloplax have been found on wood from the deep seas of the Northeast Pacific off the United States and in the Tongue of the Ocean (a deep ocean trench) off the Bahamas. The scientists that described the first specimens of Xyloplax indicated that it was clearly an echinoderm. However, because Xyloplax was so distinctive compared to other echinoderms, it represented a previously undiscovered lineage—that is, a sixth class of extant echinoderms. Lineages of echinoderms are important because echinoderms share a common ancestor with other deuterostomes, including chordates. Because of this link, echinoderms provide clues to understanding the tree of life and the deep history of our species.
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