Platyzoa
{{Short description|Superphylum of unsegmented animals}}
{{Automatic taxobox
| fossil_range = {{Fossil range| Cambrian|Recent}}
| image = Bedford's Flatworm.jpg
| image_caption = Pseudobiceros bedfordi (Bedford's flatworm)
| display_parents = 6
| taxon = Platyzoa
| authority = Cavalier-Smith, 1998
| subdivision_ranks = Phyla
| subdivision = * Gastrotricha
- Gnathifera (unranked)
- Gnathostomulida
- Micrognathozoa
- Syndermata (Rotifera)
- including Acanthocephala
- Chaetognatha
- {{extinct}}Amiskwia (not placed in a phylum)
- {{extinct}}Timorebestia (stem-chaetognath)
- {{extinct}}Inquicus
- {{extinct}}Nectocarididae?
- Platyhelminthes
- Mesozoa (unranked)?
- Dicyemida
- ?Monoblastozoa
- ?Orthonectida
}}
The "Platyzoa" {{IPAc-en|ˌ|p|l|æ|t|ᵻ|ˈ|z|oʊ|.|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. Later it has been described as paraphyletic, containing the Rouphozoa and the Gnathifera. Since 2022 it is believed that Platyozoa are monophyletic and also includes Mesozoa.
Phyla
{{See also|List of bilaterial animal orders}}
One scheme placed the following phyla in Platyzoa:
- Rouphozoa
- Platyhelminthes
- Gastrotricha
- Gnathifera{{Cite web |url=http://www.zmuc.dk/InverWeb/Dyr/Limnognathia/phylogeny/phylogeny_UK.htm |title=Limnognathia |last=Sørensen |first=Martin |date=14 December 2005 |publisher=Zoological Museum, University of Copenhagen |access-date=28 December 2016 |archive-url=https://web.archive.org/web/20181224120201/http://www.zmuc.dk/InverWeb/Dyr/Limnognathia/phylogeny/phylogeny_UK.htm |archive-date=24 December 2018 |url-status=dead }}
- Syndermata
- Rotifera
- Seisonida
- 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.{{cite web |url=http://science.kennesaw.edu/~jdirnber/InvertZoo/Tree/Explanations.html |title=Explanations.html |access-date=2009-06-28 |archive-url=https://web.archive.org/web/20130207074145/http://science.kennesaw.edu/%7Ejdirnber/InvertZoo/Tree/Explanations.html |archive-date=2013-02-07 |url-status=dead }}
Classification
The Platyzoa are close relatives of the Lophotrochozoa. Together the two make up the Spiralia.{{cladogram|clades={{clade
|label1=Spiralia
|1={{clade
|1=Gnathifera
|label2=Platytrochozoa
|2={{clade
|1={{clade
|label1=Rouphozoa
|1={{clade
|1=Gastrotricha
}}
|2=Mesozoa
}}
}}
}}
}}|style=font-size:80%;line-height:80%}}
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.[http://rickbrusca.com/http___www.rickbrusca.com_index.html/Invertebrates,_3rd_Ed._files/Ch%2016%20Gnathifera.pdf Gnathifera - Richard C. Brusca]
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).{{Cite journal|last=Struck|first=Torsten H.|last2=Wey-Fabrizius|first2=Alexandra R.|last3=Golombek|first3=Anja|last4=Hering|first4=Lars|last5=Weigert|first5=Anne|last6=Bleidorn|first6=Christoph|last7=Klebow|first7=Sabrina|last8=Iakovenko|first8=Nataliia|last9=Hausdorf|first9=Bernhard|date=2014-07-01|title=Platyzoan Paraphyly Based on Phylogenomic Data Supports a Noncoelomate Ancestry of Spiralia|journal=Molecular Biology and Evolution|language=en|volume=31|issue=7|pages=1833–1849|doi=10.1093/molbev/msu143|issn=0737-4038|pmid=24748651|doi-access=free}} The Lophotrochozoa and Rouphozoa are then named the Platytrochozoa. This makes the Platyzoa a paraphyletic group.{{clarify|date=April 2023|Cladogram doesn't say "Platyzoa" anywhere, and the ssister to the Rouphozoa in the tree is named "Mesozoa", which does not seem to be a synonym of Platyzoa?}}
References
{{Reflist}}
- [http://sn2000.taxonomy.nl/Taxonomicon/TaxonTree.aspx?id=126691 The Taxonomicon - Taxon: Infrakingdom Platyzoa Cavalier-Smith, 1998] - retrieved January 31, 2006
- [http://taylorandfrancis.metapress.com/(karlsa55kkmi3nmox1xujfbv)/app/home/contribution.asp?referrer=parent&backto=issue,9,14;journal,32,42;linkingpublicationresults,1:102493,1 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
- [https://www.doi.org/10.1111/j.1096-0031.2001.tb00116.x Myzostomida Are Not Annelids: Molecular and Morphological Support for a Clade of Animals with Anterior Sperm Flagella] - retrieved January 31, 2006
- [https://web.archive.org/web/20050906125054/http://www.botany.utoronto.ca/ResearchLabs/guttmanLab/Bot1700/Giribet_2002_MPE(24)345.pdf Current advances in the phylogenetic reconstruction of metazoan evolution. A new paradigm for the Cambrian explosion?] - retrieved January 31, 2006
{{Animalia}}
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