Meeting Abstract

56.1  Tuesday, Jan. 6  Molecular phylogenetics and taxonomy of pilidiophoran nemerteans: tackling a can of worms. SCHWARTZ, M.L.*; NORENBURG, J.L.; Seattle University, WA; Smithsonian Insitution, Washington, DC norenburgj@si.edu

Pilidiophoran taxonomy is based on ad hoc morphological character combinations and perceptions of taxa by experts, and it has taken, until recently, only very limited advantage of objective phylogenetic methods. More than half of the approximate 420 species in the group are allocated to three mega-genera; the remainder to about 80 mostly monotypic genera. Here we present the most comprehensive phylogenetic hypotheses of pilidiophoran relationships to date, based on 76 taxa, sequence data for three genes, and more than 100 morphological characters. Pilidiophora is monophyletic, with several well-supported clades, including clades of the genera Baseodiscus and Notospermus, a clade of orange-capped worms, and a small clade of traditional Cerebratulus species. However, relationships between stable clades remain problematic, because branching pattern and intermediate nodes are not well resolved. It is not surprising that morphology is one source of conflict, but molecular data also have been surprisingly inconsistent. Phylogenies derived from 16S rDNA and COI data partitions are poorly resolved and do not recover clades that are well supported in other analyses. However, the partition-addition-bootstrap-alteration (PABA) approach reinforced the usefulness of multiple data sets; two or more data partitions always substantially increased overall phylogenetic signal and resolution. These results provide ample evidence that pilidiophoran taxonomy poorly reflects ancestry and that the three mega-genera urgently need revision.