18S RIBOSOMAL-RNA SUGGESTS THAT ENTOPROCTA ARE PROTOSTOMES, UNRELATEDTO ECTOPROCTA

The Ento- and Ectoprocta are sometimes placed together in the Bryozoa, which have variously been regarded as proto- or deuterostomes. Howeve r, Entoprocta have also been allied to the pseudocoelomates, while Ect oprocta are often united with the Brachiopoda and Phoronida in the (su per)phylum Lophophorata. Hence, the phylogenetic relationships of thes e taxa are still much debated. We determined complete 18S rRNA sequenc es of two entoprocts, an ectoproct, an inarticulate brachiopod, a phor onid, two annelids, and a platyhelminth. Phylogenetic analyses of thes e data show that (1) entoprocts and lophophorates have spiralian, prot ostomous affinities, (2) Ento- and Ectoprocta are not sister taxa, (3) phoronids and brachiopods form a monophyletic clade, and (4) neither Ectoprocta or Annelida appear to be monophyletic. Both deuterostomous and pseudocoelomate features may have arisen at least two times in evo lutionary history. These results advocate a Spiralia-Radialia-based cl assification rather than one based on the Protostomia-Deuterostomia co ncept.