| Platyzoa | |
|---|---|
 | |
| Pseudobiceros bedfordi (Bedford's flatworm) | |
Scientific classification | |
| Kingdom: | Animalia |
| Subkingdom: | Eumetazoa |
| Clade: | ParaHoxozoa |
| Clade: | Bilateria |
| Clade: | Nephrozoa |
| Clade: | Protostomia |
| Clade: | Spiralia |
| Superphylum: | Platyzoa Cavalier-Smith, 1998 |
| Phyla | |
The "Platyzoa"/ˌplætɪˈzoʊ.ə/ are a group ofprotostome unsegmented animals proposed byThomas Cavalier-Smith in 1998. Cavalier-Smith included in Platyzoa thephylumPlatyhelminthes (orflatworms), and a new phylum, theAcanthognatha, into which he gathered several previously described phyla of microscopicanimals. Later it has been described asparaphyletic, containing theRouphozoa and theGnathifera. Since 2022 it is believed that Platyzoa aremonophyletic and also includesMesozoa.[1]
One scheme placed the following phyla in Platyzoa:
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 areacoelomate. The other phyla have apseudocoel, and share characteristics such as the structure of their jaws andpharynx, although these have been secondarily lost in theparasitic Acanthocephala. They form a monophyletic subgroup called theGnathifera.
The name "Platyzoa" is used because most members are flat, thoughrotifers are not.[4]
The Platyzoa are close relatives of theLophotrochozoa. Together the two make up theSpiralia.
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.[5]
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).[2] The Lophotrochozoa and Rouphozoa are then named the Platytrochozoa.[2] This makes the Platyzoa a paraphyletic group.[clarification needed]