Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

  • Letter
  • Published:

Xenoturbella is a deuterostome that eats molluscs


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 Xenoturbella10,11. 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.

This is a preview of subscription content, access via your institution

Access options

Buy this article

Prices may be subject to local taxes which are calculated during checkout

Figure 1: Best ML tree found using SSU sequences.
Figure 2: Position of Xenoturbella within the deuterostomes as suggested by our analyses of SSU and mitochondrial data.

Similar content being viewed by others


  1. Westblad, E. Xenoturbella bocki n.g, n.sp, a peculiar, primitive turbellarian type. Ark. Zool. 1, 3–29 (1949)

    Google Scholar 

  2. Reisinger, E. Was ist Xenoturbella? Z. Wiss. Zool. 164, 188–198 (1960)

    Google Scholar 

  3. Pedersen, K. J. & Pedersen, L. R. Fine-structural observations on the extracellular-matrix (ecm) of Xenoturbella bocki Westblad, 1949. Acta Zool. 67, 103–113 (1986)

    Article  Google Scholar 

  4. Franzen, A. & Afzelius, B. A. The ciliated epidermis of Xenoturbella bocki (Platyhelminthes, Xenoturbellida) with some phylogenetic considerations. Zool. Scripta 16, 9–17 (1987)

    Article  Google Scholar 

  5. Lundin, K. The epidermal ciliary rootlets of Xenoturbella bocki (Xenoturbellida) revisited: new support for a possible kinship with the Acoelomorpha (Platyhelminthes). Zool. Scripta 27, 263–270 (1998)

    Article  Google Scholar 

  6. Lundin, K. Degenerating epidermal cells in Xenoturbella bocki (phylum uncertain), Nemertodermatida and Acoela (Platyhelminthes). Belg. J. Zool. 131, 153–157 (2001)

    Google Scholar 

  7. Pardos, F. Fine structure and function of pharynx cilia in Glossobalanus minutus Kowalewsky (Enteropneusta). Acta Zool. 69, 1–12 (1988)

    Article  Google Scholar 

  8. Ehlers, U. & Sopott-Ehlers, B. Ultrastructure of the subepidermal musculature of Xenoturbella bocki, the adelphotaxon of the Bilateria. Zoomorphology 117, 71–79 (1997)

    Article  Google Scholar 

  9. Norén, M. & Jondelius, U. Xenoturbella's molluscan relatives… Nature 390, 31–32 (1997)

    Article  ADS  Google Scholar 

  10. Israelsson, O. …and molluscan embryogenesis. Nature 390, 32 (1997)

    Article  ADS  CAS  Google Scholar 

  11. Israelsson, O. New light on the enigmatic Xenoturbella (phylum uncertain): ontogeny and phylogeny. Proc. R. Soc. Lond. B 266, 835–841 (1999)

    Article  Google Scholar 

  12. Swofford, D. L. Phylogenetic Analysis Using Parsimony (*and other methods) version 4 (Sinauer Associates, Sunderland, Massachusetts, 1998)

    Google Scholar 

  13. Huelsenbeck, J. P. & Ronquist, F. MRBAYES: Bayesian inference of phylogeny. Bioinformatics 17, 754–755 (2001)

    Article  CAS  Google Scholar 

  14. Lowe, T. M. & Eddy, S. R. tRNAscan-SE: A program for improved detection of transfer RNA genes in genomic sequence. Nucleic Acids Res. 25, 955–964 (1997)

    Article  CAS  Google Scholar 

  15. Telford, M. J., Herniou, E. A., Russell, R. B. & Littlewood, D. T. J. Changes in mitochondrial genetic codes as phylogenetic characters: two examples from the flatworms. Proc. Natl Acad. Sci. USA 97, 11359–11364 (2000)

    Article  ADS  CAS  Google Scholar 

  16. Castresana, J., Feldmaier-Fuchs, G. & Pääbo, S. Codon reassignment and amino acid composition in hemichordate mitochondria. Proc. Natl Acad. Sci. USA 95, 3703–3707 (1998)

    Article  ADS  CAS  Google Scholar 

  17. Gee, H. Before the Backbone. Views on the Origin of Vertebrates (Chapman and Hall, London, 1996)

    Google Scholar 

  18. Jeanmougin, F., Thompson, J. D., Gouy, M., Higgins, D. G. & Gibson, T. J. Multiple sequence alignment with Clustal X. Trends Biol. Sci. 23, 403–405 (1998)

    Article  CAS  Google Scholar 

  19. Maddison, D. R., Maddison, W. P. MacClade 4: Analysis of Phylogeny and Character Evolution (Sinauer Associates, Sunderland, Massachusetts, 2000)

    MATH  Google Scholar 

  20. Castresana, J. Selection of conserved blocks from multiple alignments for their use in phylogenetic analysis. Mol. Biol. Evol. 17, 540–552 (2000)

    Article  CAS  Google Scholar 

  21. Telford, M. J., Lockyer, A. E., Cartwright-Finch, C. & Littlewood, D. T. J. Combined large and small subunit ribosomal RNA phylogenies support a basal position of the acoelomorph flatworms. Proc. R. Soc. Lond. B 270, 1077–1083 (2003)

    Article  CAS  Google Scholar 

Download references


We thank M. Akam and R. Jenner for comments on the manuscript, I. Ruiz Trillo for sharing unpublished results, and the scientists of Kristineberg Marine Station for help in sample collection. We are grateful for support from the Wellcome Trust to M.J.T. and to D.T.J.L.

Author information

Authors and Affiliations


Corresponding author

Correspondence to Maximilian J. Telford.

Ethics declarations

Competing interests

The authors declare that they have no competing financial interests.

Supplementary information

Rights and permissions

Reprints and permissions

About this article

Cite this article

Bourlat, S., Nielsen, C., Lockyer, A. et al. Xenoturbella is a deuterostome that eats molluscs. Nature 424, 925–928 (2003).

Download citation

  • Received:

  • Accepted:

  • Issue Date:

  • DOI:

This article is cited by


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing