Phylogeny of the mud worm genus Marenzelleria (Polychaeta, Spionidae) inferred from mitochondrial DNA sequences

The taxonomy of the cryptic morphospecies of the mud worm genus Marenzelleria is particularly difficult and the phylogenetic relationship within the genus is unknown. Herein we reconstructed the phylogeny of all five species of this genus using sequence data of three mitochondrial genes (16SrDNA, cytochrome b, cytochrome oxidase subunit I) from 104 specimens out of 26 populations. For the three invasive species of the genus, Marenzelleria neglecta, M. viridis and M. arctia, individuals from native populations as well as from recently invaded populations were included. Nuclear 18S rDNA sequences were used to evaluate the appropriate outgroup taxon among several spionid polychaete species. The results supported the monophyly of Marenzelleria, and Malacoceros fuliginosus was found to be a suitable outgroup for the analysis of the mitochondrial gene segments. All phylogenetic reconstructions revealed a basal position of M. arctia and M. wireni, which have primarily Arctic distribution, with M. arctia obtaining the most basal position. Together with the present-day distribution of the species, this indicates an origin of the genus in the Arctic region. The relationship of the species M. neglecta, M. viridis and M. bastropi could not be resolved sufficiently due to genealogical discordance that might reflect relatively young cladogenetic events.