Meeting Abstract

136.5  Monday, Jan. 7  First Xenoturbella spp. (Xenoturbellida) from the Pacific ROUSE, GW*; WILSON, NG; VRIJENHOEK, RC; Scripps Institution of Oceanography; Australian Museum; Monterey Bay Aquarium and Research Institute grouse@ucsd.edu

Xenoturbella is an enigmatic bilaterian taxon of animals that currently contains two nominal species, Xenoturbella bocki Westblad 1949 and Xenoturbella westbladi Israelsson 1999, both from shallow waters off the Swedish west coast and reaching about 3 cm in length. Evidence from mitochondrial cytochrome C oxidase I sequences suggest that these two in fact represent a single species, Xenoturbella bocki. Following initial placement as close to acoel flatworms, the position of Xenoturbella amongst Metazoa has varied considerably. They have been considered to be derived molluscs, deuterostomes, or with acoels as basal bilaterian animals. The most recent study places Xenoturbella and Acoelomorpha as a clade that is sister to Ambulacraria (Hemichordata and Echinodermata) among the deuterostomes. Here we report the discovery, via Remote Operated Vehicles, of three new species of Xenoturbella from deep waters of the eastern Pacific Ocean. One species is closely related to Xenoturbella bocki and is of a similar size, and was found near a whalefall at 600 m depth in Monterey Canyon (California). The second species is much larger (~10 cm), and was found in a vesicomyid clam field at ~3000 m depth in Monterey Canyon. This species was also found at 2000 m. in the Guaymas Basin (Gulf of California, Mexico). The third species, also large, was also found in the Guaymas Basin at 2000 m. Evidence from live observations, morphology and molecular sequence analyses are presented. It is likely that this dramatic expansion in the known diversity of Xenoturbella will provide further data to stabilize their systematic placement within Metazoa.