MAXMEN, A.B.*; CUTLER, E.; GIRIBET, G.; Harvard University; Harvard University; Harvard University: Evolutionary relationships within the protostome phylum Sipuncula; A molecular analysis of ribosomal genes and histone H3 sequence data

The internal phylogeny of the phylum Sipuncula is investigated by means of DNA sequence data from three nuclear markers, two ribosomal genes (18S rRNA and the D3 expansion fragment of 28S rRNA), and one protein-coding gene, histone H3. Phylogenetic analysis via direct optimization of DNA sequence data choosing parsimony as optimality criterion is executed for twelve combinations of parameter sets accounting for different indel costs and transversion/transition cost ratios in a sensitivity analysis framework. Nodal support is measured by Bremer support values and parsimony jackknifing. Results from the differnet partitions are highly congruent, and the combined analysis for the parameter set that minimizes overall incongruence supports monophyly of Sipuncula, but non-monophyly of several higher taxa recognized for the phylum. Mostly responsible for this is the split of the family Sipunculidae into three main lineages, with the genus Sipunculus being the sister group to the remaining sipunculans, the genus Phascolopsis nesting within the Golfiniiformes, and the genus Siphonosoma being associated to the Phascolosomatidea. Other interesting results are the position of Phascolion within Golfingiidae, and the position of Antillesoma within Aspidosiphonidae. Monophyly of the genera with multiple representatives: Themiste, Aspidosiphon, and Phascolosoma is well supported, but not the monophyly of the genera Nephasoma or Golfingia. Interesting phylogeographic questions arise from analysis of multiple representatives of a few species.