4-536: The " Platyzoa " / ˌ p l æ t ɪ 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
8-618: The Rouphozoa and the Gnathifera . Since 2022 it is believed that Platyozoa are monophyletic and also includes Mesozoa . 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 are acoelomate . The other phyla have a pseudocoel , and share characteristics such as
12-582: 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. The Platyzoa are close relatives of the Lophotrochozoa . Together the two make up the Spiralia . Gnathifera Gastrotricha Platyhelminthes Mesozoa Lophotrochozoa Syndermata
16-654: 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. 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). The Lophotrochozoa and Rouphozoa are then named the Platytrochozoa. This makes
#228771