Eutrochozoa

From Palaeos

Protostomia
`--o Lophotrochozoa [or Spiralia]
   `--+--Bryozoa [Ectoprocta]
      |--Platyzoa
      `--o Trochozoa 
         |==Coeloscleritophora† ("Procoelomata†")
         |--Nemertea [Nemertinea]
         |--o Eutrochozoa
         |  |?-Tullimonsterida †
         |  |--Mollusca
         |  |--Hyolitha †
         |  |--Sipuncula 
         |  `--Annelida
         `--o Brachiozoa
            |--Phoronida 
            `--Brachiopoda

The Eutrochozoa is a rather poorly-defined group of protostome animals. At its most exclusive, it at least includes Mollusca, Sipuncula and Annelida (with the last here including Echiura and Pogonophora), but other phyla such as Nemertea and Entoprocta have also been associated with this group in the past. Eutrochozoa are currently regarded by most authors as part of the clade Lophotrochozoa, but their monophyly within Lophotrochozoa is uncertain - for instance, Conway Morris & Peel (1995) placed Annelida closer to Brachiozoa than Mollusca, while a recent major molecular analysis of Annelida (Rousset, et al., 2007) failed to resolve it as monophyletic relative to Mollusca, Sipuncula, Nemertea or Brachiozoa (though the authors did not regard this as likely to reflect the true phylogeny).

Eutrochozoa are characterised by spiral cleavage (Valentine, 1997), a trochophore larva passing through prototroch and telotroch stages, and nephridiopores (Eernisse et al., 1992).

References

Conway Morris, S., & J. S. Peel. 1995. Articulated halkieriids from the lower Cambrian of North Greenland and their role in early protostome evolution. Philosophical Transations of the Royal Society of London B 447: 305-358.

Eernisse, D. J., J. S. Albert & F. E. Anderson. 1992. Annelida and Arthropoda are not sister taxa: a phylogenetic analysis of spiralian metazoan morphology. Systematic Biology 41 (3): 305-330.

Rousset, V., F. Pleijel, G. W. Rouse, C. Erséus & M. E. Siddall. 2007. A molecular phylogeny of annelids. Cladistics 23: 41-63.

Valentine, J. W. 1997. Cleavage patterns and the topology of the metazoan tree of life. Proceedings of the National Academy of Sciences of the USA 94: 8001-8005.

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