Phylogeny of Nemertea with special interest in the placement of diversity from Far East Russia and northeast Asia

Recent investigations, based mostly on molecular data, have unraveled the evolutionary history of several common ribbon worm (phylum Nemertea) species and solidified the taxonomic status of many higher taxa within the group. However, a large proportion of enigmatic species have yet to be placed in a phylogenetic framework. We investigated the phylogenetic positions of 26 novel and/or perplexing nemertean species from the Sea of Okhotsk, the Sea of Japan, the Kuril–Kamchatka Trench, and Vietnam (including the first record of a reptant nemertean from the Far East seas of Russia). We conducted both maximum likelihood and parsimony analyses, utilizing four molecular loci—mitochondrial COI and 16S rRNA, as well as nuclear 18S rRNA and 28S rRNA—finding that the current classification for most of these species is corroborated by their phylogenetic placement. We then discuss the evolution of some unique morphological traits possessed by some of these species, using the molecular phylogeny as a backbone for our general conclusions.