Pseudobiceros bedfordi, a flatworm ( Platyhelminthes )

The flatworm -like ( Platyzoa ) are over- strain of worm-like invertebrate animals.


There are simply built Urmünder ( Protostomia ) without secondary body cavity ( coelom ). Protonephridia, the simplest excretory organs, are also present in adult animals. Most types of Platyzoa are very small, often only be seen with a microscope. Only among the flatworms and parasitic worms scratch there are species the lengths of half a meter and can achieve more.


Considering the currently discussed redistricting Protostomia they are most likely a sub-group ( subtaxon ) of the Lophotrochozoa, they could phylogenetically but also be a sister group of Lophotrochozoa. With up to eight strains (see the cladogram below ) they are by far the largest suggested subtaxon the Lophotrochozoa. The " Platyzoa " were drawn only in the late 1990s as a possible community of descent into consideration, but molecular biological results are not yet clear on this. For example, could the jaw carrier ( Gnathifera ), which should be a reasonable subset of morphologically detailed " Platyzoa " are not yet confirmed by molecular genetic methods. Only the sister group relation between the cup and the worms Cycliophora and the paraphyly of rotifers in relation to the scratch worms are currently considered reasonably well protected. The exact relationships of the other groups and the classification of the " Platyzoa " as a community of descent, however, are controversial.

The possible kinship relationships cladogram shows the following:

Flatworms ( Platyhelminthes )

Bauchhärlinge ( Gastrotricha )

Cup animals ( Entoprocta )


Gnathostomulids ( Gnathostomulida )





Scratch worms ( Acanthocephala )

Monogononta, Bdelloida and Seisonida are Untertaxa the paraphyletic rotifers ( Rotifera ). The common taxon of rotifers and scratch worms called Syndermata.