18S RIBOSOMAL-RNA DATA INDICATE THAT ASCHELMINTHES ARE POLYPHYLETIC IN ORIGIN AND CONSIST OF AT LEAST 3 DISTINCT CLADES

The Aschelminthes is a collection of at least eight animal phyla, hist orically grouped together because the absence of a true body cavity wa s perceived as a pseudocoelom. Analyses of 18S rRNA sequences from six Aschelminth phyla (including four previously unpublished sequences) s upport polyphyly for the Aschelminthes. at least three distinct groups of Aschelminthes were detected: the Priapulida among the protostomes, the Rotifera-Acanthocephala as a sister group to the protostomes, and the Nematoda as a basal group to the triploblastic Eumetazoa.