Phylogeny of Priapulida.

The systematic position of the small invertebrate group, Priapulida, is uncertain. In more recent publications they are classified usually as pseudocoelomates in the division Aschelminthes. A histological investigation of Priapulus caudatus, a widely distributed species, reveals the body cavity to be a coelom, its lining a peritoneum. These features, and others, indicate the priapulids to be. coelomates rather than pseudocoelomates. Unique morphology perhaps qualifies the group for the status of phylum.