Comparative mitogenomics and biodiversity studies of Nemertea

Abstract This study presents genome skimming data from 20 nemertean specimens collected globally encompassing diverse habitats. Complete mitochondrial genomes were sequenced and assembled for all species, and phylogenetic analyses of the relationships recovered their evolutionary positions. Due to the limited presence of external morphological traits and a lack of previously published sequence data, it was not possible to make species-level identifications for several of the samples. The large scale analysis of mitochondrial gene order in Nemertea shows that this phylum has a comparatively conserved mitochondrial genome. Heteronemertea and some palaenemertean genera have the protein-coding gene order of the ancestral lophotrochozoans, while Hoplonemertea and Cephalothrix Örsted, 1843, (Archinemertea) exhibit gene translocations. In total, three protein-coding gene orders and five tRNA gene orders have been described from Nemertea. In addition, analysis of mt genomes and the nuclear 28S recovered a possible inter-species hybrid with an anomalous genome size. Genome skimming offers a fast and convenient method to analyze nemertean mt genomes on a large scale. Next generation sequencing offers a promising future for nemertean research as it opens new possibilities to study nemertean evolution.