View source for 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 = [[Thomas Cavalier-Smith|Cavalier-Smith]], 1998
| subdivision_ranks = Phyla
| subdivision = * [[Gastrotricha]]
* '''[[Gnathifera (phylum)|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]]
** ?[[Salinella|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]] [[flatworm|Platyhelminthes]] (or [[flatworm]]s), and a new phylum, the [[Acanthognatha]], into which he gathered several previously described phyla of microscopic [[Animal|animals]]. Later it has been described as [[paraphyletic]], containing the [[Rouphozoa]] and the [[Gnathifera (phylum)|Gnathifera]]. Since 2022 it is believed that Platyozoa are [[Monophyly|monophyletic]] and also includes [[Mesozoa]].

==Phyla==
{{See also|List of bilaterial animal orders}}
One scheme placed the following phyla in Platyzoa:

* [[Rouphozoa]]<ref name="torsten"/>
** [[Flatworm|Platyhelminthes]]
** [[Gastrotrich]]a
* [[Gnathifera (phylum)|Gnathifera]]<ref name="sorenson">{{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 }}</ref>
** [[Syndermata]]
*** [[Rotifer]]a
*** [[Seisonida]]
** [[Acanthocephala]]
** [[Gnathostomulid]]a
** [[Limnognathia|Micrognathozoa]]
** [[Symbion|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 [[body cavity|acoelomate]].  The other phyla have a [[Body cavity#Pseudocoel|pseudocoel]], and share characteristics such as the structure of their jaws and [[pharynx]], although these have been secondarily lost in the [[Parasite|parasitic]] Acanthocephala.  They form a monophyletic subgroup called the [[Gnathifera (phylum)|Gnathifera]].

The name "Platyzoa" is used because most members are flat, though [[rotifer]]s are not.<ref name="urlExplanations.html">{{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 }}</ref>

==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 (clade)|Gnathifera]]
     |label2=[[Platytrochozoa]]
     |2={{clade
        |1={{clade
        |label1=[[Rouphozoa]]
        |1={{clade
            |1=[[Gastrotricha]]
            |2=[[Platyhelminthes]]
        }}
        |2=[[Mesozoa]]
        }}
        |2=[[Lophotrochozoa]]
      }}
   }}
}}|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.<ref>[http://rickbrusca.com/http___www.rickbrusca.com_index.html/Invertebrates,_3rd_Ed._files/Ch%2016%20Gnathifera.pdf Gnathifera - Richard C. Brusca]</ref>

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).<ref name="torsten">{{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}}</ref> The Lophotrochozoa and  Rouphozoa are then named the Platytrochozoa.<ref name="torsten"/> 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}}
{{Taxonbar|from=Q46851}}

[[Category:Platyzoa| ]]
[[Category:Superphyla]]
[[Category:Spiralia]]