HALANYCH, K. M.; PASSAMANECK, Y.; Auburn Univ.; Woods Hole Oceanographic Insitution: Recent Progress on Resolving Lophotrochozoan Phylogeny

The Lophotrochozoa, including mollusks, annelids, brachiopods, flatworms and their allies, encompasses the greatest amount of body plan diversity of the three major bilaterian lineages. Within the clade interphyletic relationships are poorly resolved with most previous analyses limited to morphology and/or small ribosomal subunit (SSU) data. To further elucidate lophotrochozoan evolutionary history and body plan diversification, we have analyzed DNA sequences of the large-subunit ribosomal RNA (LSU) gene from a diversity of recognized phyla. Unlike SSU data alone, the LSU and combined LSU + SSU datasets recover the monophyly of most recognized lophotrochozoan phyla, a prerequisite of evaluating interphyletic relationships. The data show Bryozoa diverged prior to the diversification of other lophotrochozoans, suggesting a cryptic early evolution of the lineage leading to bryozoans. Lophophorata, an exclusive Bryozoa/Brachiopoda/Phoronida clade, is significantly rejected as is a Bryozoa/Entoprocta clade. Contrary to previous reports, Platyzoa (including platyhelminthes, rotifers, and acanthocephalans) appears to be derived within lophotrochoazoans rather than a sister group to the Lophotrochozoa. In the LSU and LSU + SSU data, entoprocts and cycliophorans form a clade sister to Platyzoa.