Complete mitochondrial genome and the phylogenetic position of a new Annelida species belonging to the genus Syllis [version 1; peer review: 1 not approved]

The family Syllidae is the most taxonomically complex of the phylum Annelida. Although the gene order in the phylum Annelida's mitochondrial DNA (mtDNA) is well conserved, several exceptional cases have been reported. In this study, we describe the mitochondrial genome of a Syllis sp. that is 17,092 bp in length and contains 13 mitochondrial protein-coding genes (PCGs), 23 transfer RNA (tRNA) genes, including two tRNA-M, two ribosomal RNA (rRNA) genes, and a putative control region between tRNA-W and tRNA-G distinguished by a single short noncoding region. However, the gene order is not similar to those of other species in the family Syllidae. Phylogenetic analyses of 18S rRNA and 13 PCGs sequences demonstrated that this worm was clustered with other Syllis species in the family Syllidae. This is the first study to reveal the complete mitochondrial genome sequence of a previously unidentified Syllissp. improving our understanding of the molecular biological characteristics of the poorly known genus Syllis.