Organisms Diversity & Evolution

, Volume 11, Issue 2, pp 151–172 | Cite as

Higher-level metazoan relationships: recent progress and remaining questions

  • Gregory D. Edgecombe
  • Gonzalo Giribet
  • Casey W. Dunn
  • Andreas Hejnol
  • Reinhardt M. Kristensen
  • Ricardo C. Neves
  • Greg W. Rouse
  • Katrine Worsaae
  • Martin V. Sørensen
Review

Abstract

Metazoa comprises 35–40 phyla that include some 1.3 million described species. Phylogenetic analyses of metazoan interrelationships have progressed in the past two decades from those based on morphology and/or targeted-gene approaches using single and then multiple loci to the more recent phylogenomic approaches that use hundreds or thousands of genes from genome and transcriptome sequencing projects. A stable core of the tree for bilaterian animals is now at hand, and instability and conflict are becoming restricted to a key set of important but contentious relationships. Acoelomorph flatworms (Acoela + Nemertodermatida) and Xenoturbella are sister groups. The position of this clade remains controversial, with different analyses supporting either a sister-group relation to other bilaterians (=Nephrozoa, composed of Protostomia and Deuterostomia) or membership in Deuterostomia. The main clades of deuterostomes (Ambulacraria and Chordata) and protostomes (Ecdysozoa and Spiralia) are recovered in numerous analyses based on varied molecular samples, and also receive anatomical and developmental support. Outstanding issues in protostome phylogenetics are the position of Chaetognatha within the protostome clade, and the monophyly of a group of spiralians collectively named Platyzoa. In contrast to the broad consensus over key questions in bilaterian phylogeny, the relationships of the five main metazoan lineages—Porifera, Ctenophora, Placozoa, Cnidaria and Bilateria—remain subject to conflicting topologies according to different taxonomic samples and analytical approaches. Whether deep bilaterian divergences such as the split between protostome and deuterostome clades date to the Cryogenian or Ediacaran (and, thus, the extent to which the pre-Cambrian fossil record is incomplete) is sensitive to dating methodology.

Keywords

Phylogenomics Expressed sequence tags Animal evolution Bilateria Ecdysozoa Spiralia 

Supplementary material

13127_2011_44_MOESM1_ESM.doc (70 kb)
ESM 1(DOC 70 kb)

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Copyright information

© Gesellschaft für Biologische Systematik 2011

Authors and Affiliations

  • Gregory D. Edgecombe
    • 1
  • Gonzalo Giribet
    • 2
  • Casey W. Dunn
    • 3
  • Andreas Hejnol
    • 4
  • Reinhardt M. Kristensen
    • 5
  • Ricardo C. Neves
    • 4
  • Greg W. Rouse
    • 6
  • Katrine Worsaae
    • 7
  • Martin V. Sørensen
    • 5
  1. 1.Department of PalaeontologyThe Natural History MuseumLondonUK
  2. 2.Museum of Comparative Zoology, Department of Organismic and Evolutionary BiologyHarvard UniversityCambridgeUSA
  3. 3.Department of Ecology and Evolutionary BiologyBrown UniversityProvidenceUSA
  4. 4.Sars International Centre for Marine Molecular BiologyUniversity of BergenBergenNorway
  5. 5.Natural History Museum of DenmarkUniversity of CopenhagenCopenhagenDenmark
  6. 6.Scripps Institution of OceanographyLa JollaUSA
  7. 7.Marine Biological SectionUniversity of CopenhagenHelsingørDenmark

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