POLYPHYLY OF SCLEROSPONGES (PORIFERA, DEMOSPONGIAE) SUPPORTED BY 28S RIBOSOMAL SEQUENCES

To test the competing hypotheses of polyphyly and monophyly of ''scler osponges,'' sequences from the 5' end of 28S ribosomal RNA were obtain ed for Astrosclera willeyana, Acanthochaetetes wellsi, and six other d emosponge species. Phylogenetic relationships deduced from parsimony a nd neighbor-joining analyses suggest that these sclerosponges belong t o two different orders of Demospongiae: Astrosclera willeyana, being c losely related to the Agelasidae, belongs to the Agelasida, Acanthocha etetes wellsi, being closely related to the Spirastrellidae, belongs t o the Hadromerida. These results contradict the hypothesis that sclero sponges are monophyletic and imply that a massive calcareous skeleton has evolved independently in several lineages of sponges.