HOOGE, M.D.*; HAYE, P.A.; KORNFIELD, I.; LITVAITIS, M.K.; TYLER, S.: Phylogenetic relationships within the Acoela (Acoelomorpha, Platyhelminthes) inferred from 18S rDNA sequences

We used newly obtained nuclear 18S rDNA sequences from 18 acoels in combination with sequences obtained from Genbank to create a dataset representing 10 acoel families, in which over 90% of the described acoels are presently classified. While the tree topology generated by our phylogenetic analyses differs from the presently held systematic scheme of the Acoela, these differences can be validated with morphological evidence. Among our findings is the apparent polyphyly of the largest acoel family, Convolutidae. The type species of the family, Convoluta convoluta, groups in a robust clade containing the largest members of the Acoela (> 2 mm in length), including other large convolutids and representatives of the Anaperidae, and Sagittiferidae . The smaller and more cylindrically shaped members of the Convolutidae, including another species of the genus Convoluta, cluster together in a separate robust clade. While we were not able to resolve the relationships among genera within families using 18S rDNA, it appears that this gene is effective in clarifying familial level relationships within the Acoela.