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Platyzoa

The Platyzoa (pronounced /ˌplætɨˈzoʊə/) are a group of protostome animals proposed by Thomas Cavalier-Smith in 1998. Cavalier-Smith included in Platyzoa the Phylum Platyhelminthes or flatworms, and a new phylum, Acanthognatha, into which he gathered several previously described phyla of microscopic animals. Subsequent studies have supported Platyzoa as a clade, a monophyletic group of organisms with a common ancestor, while differing on the phyla included and on relationships within Platyzoa.

One current scheme places the following traditional phyla in Platyzoa:

• Platyhelminthes
• Gastrotricha
• Gnathifera
  • Rotifera
  • Acanthocephala
  • Gnathostomulida
  • Micrognathozoa
  • Cycliophora

The Platyhelminthes and Gastrotricha are acoelomate. The other phyla have a pseudocoel, and share characteristics such as the structure of their jaws and pharynx, although these have been secondarily lost in the parasitic Acanthocephala. They form a monophyletic subgroup called the Gnathifera.

The Platyzoa are close relatives of the Lophotrochozoa, and are sometimes included in that group. Together the two make up the Spiralia.

References

• The Taxonomicon - Taxon: Infrakingdom Platyzoa Cavalier-Smith, 1998 - retrieved January 31, 2006
• The interrelationships of metazoan parasites: a review of phylum- and higher-level hypotheses from recent morphological and molecular phylogenetic analyses - retrieved January 31, 2006
• Triploblastic Relationships with Emphasis on the Acoelomates and the Position of Gnathostomulida, Cycliophora, Plathelminthes, and Chaetognatha: A Combined Approach of 18S rDNA Sequences and Morphology - retrieved January 31, 2006
• Myzostomida Are Not Annelids: Molecular and Morphological Support for a Clade of Animals with Anterior Sperm Flagella - retrieved January 31, 2006
• Current advances in the phylogenetic reconstruction of metazoan evolution. A new paradigm for the Cambrian explosion? - retrieved January 31, 2006