Testing the new animal phylogeny: a phylum level molecular analysis of the animal kingdom.

The new animal phylogeny inferred from ribosomal genes some years ago has prompted a number of radical rearrangements of the traditional, morphology based metazoan tree. The two main bilaterian clades, Deuterostomia and Protostomia, find strong support, but the protostomes consist of two sister groups, Ecdysozoa and Lophotrochozoa, not seen in morphology based trees. Although widely accepted, not all recent molecular phylogenetic analyses have supported the tripartite structure of the new animal phylogeny. Furthermore, even if the small ribosomal subunit (SSU) based phylogeny is correct, there is a frustrating lack of resolution of relationships between the phyla that make up the three clades of this tree. To address this issue, we have assembled a dataset including a large number of aligned sequence positions as well as a broad sampling of metazoan phyla. Our dataset consists of sequence data from ribosomal and mitochondrial genes combined with new data from protein coding genes (5139 amino acid and 3524 nucleotide positions in total) from 37 representative taxa sampled across the Metazoa. Our data show strong support for the basic structure of the new animal phylogeny as well as for the Mandibulata including Myriapoda. We also provide some resolution within the Lophotrochozoa, where we confirm support for a monophyletic clade of Echiura, Sipuncula and Annelida and surprising evidence of a close relationship between Brachiopoda and Nemertea.