The Complete Mitochondrial Genome of Mytilisepta virgata (Mollusca: Bivalvia), Novel Gene Rearrangements, and the Phylogenetic Relationships of Mytilidae

The circular mitochondrial genome of Mytilisepta virgata spans 14,713 bp, which contains 13 protein-coding genes (PCGs), 2 ribosomal RNA genes, and 22 transfer RNA genes. Analysis of the 13 PCGs reveals that the mitochondrial gene arrangement of Mytilisepta is relatively conserved at the genus level. The location of the atp8 gene in Mytilisepta keenae differs from that of other species. However, compared with the putative molluscan ancestral gene order, M. virgata exhibits a high level of rearrangement. We constructed phylogenetic trees based on concatenated 12 PCGs from Mytilidae. As a result, we found that M. virgata is in the same clade as other Mytilisepta spp. The result of estimated divergence times revealed that M. virgata and M. keenae diverged around the early Paleogene period, although the oldest Mytilisepta fossil was from the late or upper Eocene period. Our results provide robust statistical evidence for a sister-group relationship within Mytilida. The findings not only confirm previous results, but also provide valuable insights into the evolutionary history of Mytilidae.