DNA taxonomy of Swedish Catenulida (Platyhelminthes) and a phylogenetic framework for catenulid classification

Specimens of Catenulida were collected at 34 localities in Sweden. We used 18S rDNA, 28S rDNA, ITS-5.8S, and cytochrome oxidase I (COI) nucleotide sequences to infer phylogeny from parsimony jackknifing and Bayesian analysis. Our dataset contained 74 ingroup terminals and 5111 characters. The results show a basal split between a clade consisting of the marine Retronectidae+the limnic Catenulidae, and a second clade consisting of the limnic Stenostomidae. The hypothesis of the marine Retronectidae as the sister group of the limnic Catenulida is rejected. The recently introduced genus Anokkostenostomum Noreña, Damborenea & Brusa, 2005 results as non-monophyletic, and Suomina Marcus, 1945 as a group inside Catenula Dugès, 1832. Therefore, we propose to render Anokkostenostomum a new junior synonym of Stenostomum Schmidt, 1848, and Suomina a new junior synonym of Catenula. Consequently, the new combinations Catenula evelinae (Marcus, 1945), Catenula sawayai (Marcus, 1945), and Catenula turgida (Zacharias, 1902) are proposed, and 14 species are returned to their original genus, Stenostomum. The molecular phylogenetic hypothesis is used to identify and discriminate catenulid species. In our material, we found 12 species of Catenulida new to Sweden, and four species new to science, all of which are distinguishable by morphological characters.