18S rRNA data indicate that Aschelminthes are polyphyletic in origin and consist of at least three distinct clades

The Aschelminthes is a collection of at least eight animal phyla,historically grouped together because the absence of a true body cavity wasperceived as a pseudocoelom. Analyses of 18S rRNA sequences from sixAschelminth phyla (including four previously unpublished sequences) supportpolyphyly for the Aschelminthes. At least three distinct groups ofAschelminthes were detected: the Priapulida among the protostomes, theRotifera-Acanthocephala as a sister group to the protostomes, and theNematoda as a basal group to the triploblastic Eumetazoa.