Overview

Brief Summary

Deuterostomia is a major subgroup of animals. It is comprised of two lineages, the Chordata and Ambulacraria (Edgecombe et al. 2011, Swalla & Smith 2008).  Chordata consists of two exclusively marine groups, the fish-like lancelets (Cephalocordata) and the sea squirts, salps and relatives (Tunicata) as well as the vertebrates which include fishes, amphibians, reptiles, birds, and mammals. Ambulacraria contains the exclusively marine echinoderms (sea stars, brittle stars, sea urchins, sand dollars, sea cucumbers, and sea lilies) and hemichordates (soft-bodied benthic worm-like animals). 

Ancestrally, all deuterostomes share a special form of embryonic development characterized by (1) indeterminate cleavage (early cells retain the capacity to develop into a complete embryo), (2) the initial opening of the developing embryo (blastopore) turning into the anus, and formation of the third body layer (mesoderm) from a pouch of the embryonic gut (archenteron).  These basic developmental patterns have been modified in various ways during the evolution of deuterostome groups, making it impossible to recognize a deuterostome lineage based on ontogenetic criteria alone (Nielsen 1995).  

In addition to chordates, echinoderms, and hemichordates, several other groups have been placed in the Deuterostomia.  Lophophorates (phoronids, brachiopods, and bryozoans) and chaetognaths show a mixture of protostome and deuterostome traits. Molecular evidence indicates that they are more closely related to protostomes (Halanych et al. 1995, Helmkampf et al. 2008, Marletaz et al. 2006, Matus et al. 2006, Papillon et al. 2004, Passamaneck & Halanych 2006).  Recently, the enigmatic Xenoturbellida have been aligned with deuterostomes (Bourlat et al. 2003, 2006, 2009; Perseke et al. 2007, Philippe et al. 2007, 2011), but there is also support for an alternative position of this group with the acoelomorphs near the base of the bilaterian tree (Edgecombe et al. 2011, Hejnol et al. 2009, Lundin 1998, 2001, Nielsen 2010, Pedersen and Pedersen 1986, 1988, Raikova et al. 2000).

  • Bourlat, S. J., Nielsen, C., Lockyer, A. E., Littlewood, D. T., & Telford, M. J. 2003. Xenoturbella is a deuterostome that eats molluscs. Nature 424:925–928.
  • Bourlat, S. J., Juliusdottir, T., Lowe, C. J., Freeman, R., Aronowicz, J., Kirschner, M., et al. 2006. Deuterostome phylogeny reveals monophyletic chordates and the new phylum Xenoturbellida. Nature, 444:85–88.
  • Bourlat, S. J., Rota-Stabelli, O., Lanfear, R., & Telford, M. J. 2009. The mitochondrial genome structure of Xenoturbella bock (phylum Xenoturbellida) is ancestral within the deuterostomes. BMC Evolutionary Biology 9:107.
  • Edgecombe, G. D., Giribet, G., Dunn, C. W., Hejnol, A., Kristensen, R. M., Neves, R. C., Rouse, G. W., Worsaae, K., and Sørensen, M. V. 2011. Higher-level metazoan relationships: Recent progress and remaining questions. Organisms Diversity & Evolution 11(2):151-172.
  • Halanych, K. M., J. D. Bacheller, A. M. A. Aguinaldo, S. M. Liva, D. M. Hillis, and J. A. Lake. 1995. Evidence from 18S ribosomal DNA that the lophophorates are protostome animals. Science 267: 1641-1643.
  • Helmkampf, M., I. Bruchhaus and B. Hausdorf. 2008. Multigene analysis of lophophorate and chaetognath phylogenetic relationships. Molecular Phylogenetics and Evolution 46(1):206-214.
  • Hejnol, A. and Martindale, M.Q. 2009. The mouth, the anus and the blastopore: Open questions about questionable openings. In: “Animal Evolution: Genomes, Fossils and Trees”, eds. Littlewood D.T.J. & Telford, M.J., Oxford University Press. pp. 33-40.
  • Hejnol, A., Obst, M., Stamatakis, A., Ott, M., Rouse, G. W., Edgecombe, G. D., et al. 2009. Assessing the root of bilaterian animals with scalable phylogenomic methods. Proceedings of the Royal Society, Series B 276:4261–4270.
  • Lundin, K. 1998. The epidermal ciliary rootlets of Xenoturbella bocki (Xenoturbellida) revisited: new support for a possible kinship with the Acoelomorpha (Platyhelminthes). Zoologica Scripta 27: 263–270.
  • Lundin, K. 2001. Degenerating epidermal cells in Xenoturbella bocki (phylum uncertain), Nemertodermatida and Acoela (Platyhelminthes). Belgian Journal of Zoology 131:153–157.
  • Marletaz, F., E. Martin, Y. Perez, D. Papillon, X. Caubit, C. Lowe, B. Freeman, L. Fasano, C. Dossat, P. Wincker. 2006. Chaetognath phylogenomics: A protostome with deuterostome-like development. Current Biology 16: R577–578.
  • Matus, D. Q., R. R. Copley, C. W. Dunn, A. Hejnol, H. Eccleston, K. M. Halanych, M. Q. Martindale, and M. J. Telford. 2006. Broad taxon and gene sampling indicate that chaetognaths are protostomes. Current Biology 16:R575–576.
  • Nielsen, C. 1995. Animal evolution. Interrelationships of the living phyla (1st ed.). Oxford: Oxford University Press.
  • Nielsen, C. 2010. After all: Xenoturbella is an acoelomorph! Evolution & Development 12:241
  • Papillon, D., Y. Perez, X. Caubit, and Y. Le Parco. 2004. Identification of chaetognaths as protostomes is supported by the analysis of their mitochondrial genome. Molecular Biology and Evolution 21(11):2122-2129.
  • Passamaneck, Y. J. and K. M. Halanych. 2006. Lophotrochozoan phylogeny assessed with LSU and SSU data: Evidence of lophophorate polyphyly. Molecular Phylogenetics and Evolution 40(1):20-28.
  • Pedersen, K. J., & Pedersen, L. R. 1986. Fine structural observations on the extracellular matrix (ECM) of Xenoturbella bocki Westblad, 1949. Acta Zoologica 67:103–113.
  • Pedersen, K. J., & Pedersen, L. R. 1988. Ultrastructural observations on the epidermis of Xenoturbella bocki Westblad, 1949, with a discusion of epidermal cytoplasmic filament systems of invertebrates. Acta Zoologica 69:231–246.
  • Philippe, H., Brinkmann, H., Martinez, P., Riutort, M., & Baguñà, J. 2007. Acoel flatworms are not Platyhelminthes: evidence from phylogenomics. PloS ONE 8:e717.
  • Philippe, H., Brinkmann, H., Copley, R. R., Moroz, L. L., Nakano, H., Poustka, A. J., et al. 2011. Acoelomorph flatworms are deuterostomes related to Xenoturbella. Nature 470:255–258.
  • Raikova, O. I., Reuter, M., Jondelius, U., & Gustafsson, M. K. S. 2000. An immunocytochemical and ultrastructural study of the nervous and muscular systems of Xenoturbella westbladi Bilateria inc. sed.). Zoomorphology 120:107–118.
  • Swalla BJ, Smith AB. 2008. Deciphering deuterostome phylogeny: molecular, morphological and palaeontological perspectives. Philos Trans R Soc Lond B Biol Sci 363:1557-1568. 10.1098/rstb.2007.2246
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