Platyzoa

Platyzoa
Pseudobiceros bedfordi (Bedford's Flatworm)
Scientific classification
Kingdom:	Animalia
Subkingdom:	Eumetazoa
(unranked):	Bilateria
(unranked):	Protostomia
Superphylum:	Platyzoa Cavalier-Smith, 1998
Phyla
Platyhelminthes Gastrotricha Gnathifera (unranked) Rotifera Acanthocephala Gnathostomulida Micrognathozoa Cycliophora

The Platyzoa /ˌplætᵻˈzoʊ.ə/ 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.

Phyla

See also: List of bilaterial animal orders

One current scheme places the following traditional phyla in Platyzoa:

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

Characteristics

None of the Platyzoa groups have a respiration or circulation system because of their small size, flat body or parasitic lifestyle. 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 name "Platyzoa" is used because most members are flat, though rotifers are not.

Classification

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
• 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