Palaeos		Platyzoa
Ecdysozoa		Overview

BILATERIA
|--Chaetognatha
|--Deuterostomia
`--+--Spiralia
   |  |--Mollusca
   |  |--Annelida
   |  |--Brachiopoda
   |  `--Platyzoa
   `--Ecdysozoa

The free-living flatworm Dugesia gonocephala Photo by Biopix, via Encyclopaedia of Life - Platyhelminthes, Creative Commons Attribution Non-Commercial

The Platyzoa are one of the many new taxa proposed in the 1990s. It was proposed by Thomas Cavalier-Smith in 1998 as an infrakingdom for the Platyhelminthes or flatworms and several phyla of microscopic animals, and since then supported (or not) by some molecular phylogenists. It is quite likely that Platyzoa is not a clade but a paraphyletic or polyphyletic assemblage of Spiralia ("Lophotrochozoan") phyla, the members of which have undergone minaturisation and/or simplification of body plans, and hence acquired characteristics. Despite appearing to be something of a wastebasket taxon for non-ecdysozoan acoelomate or pseudocoelomate animals, some of these phyla may still constitute a monophyletic group. MAK120423