First report of the mitogenome of the invasive reef-building polychaete Ficopomatus enigmaticus (Annelida: Serpulidae) and a cryptic lineage from the Japanese Archipelago

Background The mitochondrial genomes (mitogenomes) of the family Serpulidae are characterized by a high nucleotide sequence divergence and a significant number of gene order rearrangements compared with other families within the phylum Annelida. However, only two of 50 genera of serpulids have mitogenomes already sequenced. In this study, we report the first sequencing and assembly of the complete mitogenome of Ficopomatus , thus providing further knowledge on mitochondrial gene sequences of Serpulidae. Methods and results A mitogenome of the invasive reef-building polychaete Ficopomatus enigmaticus was amplified by long PCR and sequenced using the Illumina MiSeq System. It comprised 15,853 bp and consisted of 12 protein-coding genes ( atp8 was not found), 23 tRNA, and two rRNA genes. The AT and GC skew values were infrequent when compared to annelid mitogenomes but similar to other serpulids sequenced to date (i.e., Spirobranchus and Hydroides ). The mitochondrial gene order of F. enigmaticus was highly rearranged compared to other serpulids. To amplify 16S rRNA gene sequences, we developed a 16S rRNA primer set by modifying the universal primer set 16SarL/16SbrH. We detected the 16S rRNA sequence of F . enigmaticus deposited in GenBank erroneously characterized as of serpulid origin. We reported for the first time the presence of two lineages of F . enigmaticus in Japan, which have already been identified in California, Australia, and the Mediterranean. Conclusions The first mitochondrial genome of F . enigmaticus showed a unique gene order rearrangement, corroborating the remarkable diversity in the previously reported mitogenomes of other serpulid species. The presence of the two lineages of F . enigmaticus identified for the first time in Japan represents another case of cryptic invasion. The first 16S rRNA gene sequences of F . enigmaticus obtained in the present study can be used as reference sequences in future DNA metabarcoding studies.