Aschelminthes

From Palaeos.org

Aschelminthes is often encountered as a phylum in older animal classifications, uniting most or all of the pseudocoelomate taxa. It is now universally agreed to be polyphyletic. In the Hyman classification of animals, the pseudocoelomate condition was regarded as an evolutionary intermediate between the acoelomate and true coelomate stages. With pseudocoelomate taxa often nested among coelomate taxa in modern phylogenies, it has been suggested that the pseudocoelom has arisen multiple times through simplification in the evolution of small size (many pseudocoelomates are meiofaunal).

Of the previous "Aschelminthes", the Scalidophora (including Priapulida and Kinorhyncha), Nematoda and Nematomorpha are included in Ecdysozoa. The Gastrotricha and Rotifera are probably Platyzoa (though some authors regard Gastrotricha as related to Scalidophora). The Entoprocta are of doubtful phylogenetic position, though they may be Trochozoa. Other prominent pseudocoelomate taxa that were generally not included in Aschelminthes are the Acanthocephala (Platyzoa, probably within Rotifera) and the Tardigrada (Ecdysozoa, within Panarthropoda).

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