Letters to Nature

Nature 424, 925-928 (21 August 2003) | doi:10.1038/nature01851; Received 28 February 2003; Accepted 9 June 2003

Xenoturbella is a deuterostome that eats molluscs

Sarah J. Bourlat1, Claus Nielsen2, Anne E. Lockyer3, D. Timothy J. Littlewood3 & Maximilian J. Telford1

  1. University Museum of Zoology, Department of Zoology, Downing Street, Cambridge CB2 3EJ, UK
  2. Zoological Museum (University of Copenhagen), Universitetsparken 15, DK-2100 Copenhagen, Denmark
  3. Department of Zoology, The Natural History Museum, Cromwell Road, London SW7 5BD, UK

Correspondence to: Maximilian J. Telford1 Email: mt281@cam.ac.uk
Newly determined sequences have been submitted to GenBank under accession numbers AY291292–AY291293.

Xenoturbella bocki, first described in 1949 (ref. 1), is a delicate, ciliated, marine worm with a simple body plan: it lacks a through gut, organized gonads, excretory structures and coelomic cavities. Its nervous system is a diffuse nerve net with no brain. Xenoturbella's affinities have long been obscure and it was initially linked to turbellarian flatworms1. Subsequent authors considered it variously as related to hemichordates and echinoderms owing to similarities of nerve net and epidermal ultrastructure2, 3, to acoelomorph flatworms based on body plan and ciliary ultrastructure4, 5, 6 (also shared by hemichordates7), or as among the most primitive of Bilateria8. In 1997 two papers seemed to solve this uncertainty: molecular phylogenetic analyses9 placed Xenoturbella within the bivalve molluscs, and eggs and larvae resembling those of bivalves were found within specimens of Xenoturbella 10, 11. This molluscan origin implies that all bivalve characters are lost during a radical metamorphosis into the adult Xenoturbella. Here, using data from three genes, we show that the samples in these studies were contaminated by bivalve embryos eaten by Xenoturbella and that Xenoturbella is in fact a deuterostome related to hemichordates and echinoderms.