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
Subscribe to Journal
Get full journal access for 1 year
only $3.90 per issue
All prices are NET prices.
VAT will be added later in the checkout.
Tax calculation will be finalised during checkout.
Get time limited or full article access on ReadCube.
All prices are NET prices.
Westblad, E. Xenoturbella bocki n.g, n.sp, a peculiar, primitive turbellarian type. Ark. Zool. 1, 3–29 (1949)
Reisinger, E. Was ist Xenoturbella? Z. Wiss. Zool. 164, 188–198 (1960)
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)
Franzen, A. & Afzelius, B. A. The ciliated epidermis of Xenoturbella bocki (Platyhelminthes, Xenoturbellida) with some phylogenetic considerations. Zool. Scripta 16, 9–17 (1987)
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)
Lundin, K. Degenerating epidermal cells in Xenoturbella bocki (phylum uncertain), Nemertodermatida and Acoela (Platyhelminthes). Belg. J. Zool. 131, 153–157 (2001)
Pardos, F. Fine structure and function of pharynx cilia in Glossobalanus minutus Kowalewsky (Enteropneusta). Acta Zool. 69, 1–12 (1988)
Ehlers, U. & Sopott-Ehlers, B. Ultrastructure of the subepidermal musculature of Xenoturbella bocki, the adelphotaxon of the Bilateria. Zoomorphology 117, 71–79 (1997)
Norén, M. & Jondelius, U. Xenoturbella's molluscan relatives… Nature 390, 31–32 (1997)
Israelsson, O. …and molluscan embryogenesis. Nature 390, 32 (1997)
Israelsson, O. New light on the enigmatic Xenoturbella (phylum uncertain): ontogeny and phylogeny. Proc. R. Soc. Lond. B 266, 835–841 (1999)
Swofford, D. L. Phylogenetic Analysis Using Parsimony (*and other methods) version 4 (Sinauer Associates, Sunderland, Massachusetts, 1998)
Huelsenbeck, J. P. & Ronquist, F. MRBAYES: Bayesian inference of phylogeny. Bioinformatics 17, 754–755 (2001)
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)
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)
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)
Gee, H. Before the Backbone. Views on the Origin of Vertebrates (Chapman and Hall, London, 1996)
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)
Maddison, D. R., Maddison, W. P. MacClade 4: Analysis of Phylogeny and Character Evolution (Sinauer Associates, Sunderland, Massachusetts, 2000)
Castresana, J. Selection of conserved blocks from multiple alignments for their use in phylogenetic analysis. Mol. Biol. Evol. 17, 540–552 (2000)
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)
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.
The authors declare that they have no competing financial interests.
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). https://doi.org/10.1038/nature01851
Scientific Reports (2020)
Nature Ecology & Evolution (2018)
BMC Evolutionary Biology (2017)
Organisms Diversity & Evolution (2016)