Meeting Abstract

P1.172  Friday, Jan. 4  Are acoelomorphs deuterostomes? Evidence from the genome of nemertodermatid Meara stichopi (Acoelomorpha) RYAN, JF*; BøRVE, A; HEJNOL, A; Sars International Centre for Marine Molecular Biology joseph.ryan@sars.uib.no

Despite great strides in the areas of phylogenomics and phylogenetics, the early history of the Bilateria – especially the position of acoelomorphs to the rest of animals – remains ambiguous. Experimental data from these animals holds the promise of helping to elucidate the evolutionary origin of a range of characters specific to the Bilateria including central nervous system, a through gut (mouth and anus), and mesoderm. However, the ambiguity surrounding the phylogenetic position of the Acoelomorpha makes it difficult to confidently interpret this data. Most molecular-based studies place them as sister to the rest of Bilateria (Nephrozoa), a key phylogenetic position for deducing evolutionary events that occurred in the stem of the Bilateria. However, a recent study places them within the Deuterostomia in a clade with hemichordates and echinoderms. We have sequenced, assembled, and annotated the ~250 megabase genome of the nemertodermatid Meara stichopi. We have performed phylogenomic analyses on large EST datasets that maximize taxon sampling, as well as datasets that minimize missing data by only including data from sequenced genomes. Early results from these analyses suggest that the acoelomorphs branched sister to the Nephrozoa. Our results, provide a starting point from which experimental data on Meara stichopi and other acoelomorphs can be interpreted and suggest that many important developmental ‘toolkit’ components arose after a number of complex morphological features including centralized nervous system and through gut.