Investigations into the phylogenetic position of Micrognathozoa using four molecular loci

Abstract

Micrognathozoa is the most recently discovered higher metazoan lineage. The sole known species of the group, Limnognathia maerski, was originally reported from running freshwater in Disko Island (Greenland), and has recently been recorded from the subantarctic region. Because of the presence of a particular type of jaws formed of special cuticularized rods, similar to those of gnathostomulids and rotifers, the three metazoan lineages were considered closely related, and assigned to the clade Gnathifera. A phylogenetic comparison of four molecular loci for Limnognathia maerski and other newly generated sequences of mainly acoelomate animals showed that Micrognathozoa may constitute an independent lineage from those of Gnathostomulida and Rotifera. However, the exact position of Micrognathozoa could not be determined due to the lack of support for any given relationships and due to the lack of stability in the position of Limnognathia maerski under analysis of different loci and of different parameter sets for sequence comparison. Nuclear loci tend to place Micrognathozoa with the syndermatan/cycliophoran taxa, but the addition of the mitochondrial gene cytochrome c oxidase subunit I favors a relationship of Micrognathozoa to Entoprocta.