Platyzoa

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Platyzoa
Bedford's Flatworm.jpg
Pseudobiceros bedfordi (Bedford's Flatworm)
Scientific classification edit
Kingdom: Animalia
Subkingdom: Eumetazoa
Clade: Bilateria
Clade: Nephrozoa
(unranked): Protostomia
(unranked): Spiralia
(unranked): Platyzoa
Cavalier-Smith, 1998
Phyla

The paraphyletic "Platyzoa" /ˌplætɪˈz.ə/ are a group of protostome unsegmented animals proposed by Thomas Cavalier-Smith in 1998. Cavalier-Smith included in Platyzoa the phylum Platyhelminthes (or flatworms), and a new phylum, the Acanthognatha, into which he gathered several previously described phyla of microscopic animals. More recently it has been described as paraphyletic, containing the Rouphozoa and the Gnathifera.

Phyla[edit]

One scheme placed the following phyla in Platyzoa:

Characteristics[edit]

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.[3]

Classification[edit]

The Platyzoa are close relatives of the Lophotrochozoa. Together the two make up the Spiralia.

Spiralia

Gnathifera

Platytrochozoa
Rouphozoa

Gastrotricha

Platyhelminthes

Mesozoa

Lophotrochozoa

Syndermata was a proposed clade that included Acanthocephala and rotifers, but as it appears they are not sister groups after all, the clade has been abandoned.[4]

A recent possible cladogram is shown which would show that the Lophotrochozoa emerged within Platyzoa as a sister group of the Rouphozoa (the Gastrotricha and Platyhelminthes).[1] The Lophotrochozoa and Rouphozoa are then named the Platytrochozoa.[1] This makes the Platyzoa a paraphyletic group.

References[edit]

  1. ^ a b c Struck, Torsten H.; Wey-Fabrizius, Alexandra R.; Golombek, Anja; Hering, Lars; Weigert, Anne; Bleidorn, Christoph; Klebow, Sabrina; Iakovenko, Nataliia; Hausdorf, Bernhard (2014-07-01). "Platyzoan Paraphyly Based on Phylogenomic Data Supports a Noncoelomate Ancestry of Spiralia". Molecular Biology and Evolution. 31 (7): 1833–1849. doi:10.1093/molbev/msu143. ISSN 0737-4038. PMID 24748651.
  2. ^ Sørensen, Martin (14 December 2005). "Limnognathia". Zoological Museum, University of Copenhagen.
  3. ^ "Explanations.html". Retrieved 2009-06-28.
  4. ^ Gnathifera - Richard C. Brusca