The complete mitochondrial genome of Siphonaria japonica (Heterobranchia, Siphonariidae) and its phylogenetic implications

The gastropod Siphonaria japonica, belonging to the family Siphonariidae, is an important grazer in the rocky intertidal zone of China, possessing significant ecological functions and medicinal value. To enrich the diversity of mitochondrial genomes in Gastropoda and to gain insights into their phylogenetic relationships, the mitochondrial genome of S. japonica (13,966 bp) was sequenced using next-generation sequencing. The genome comprises 13 protein-coding genes, 22 tRNA genes, and 2 rRNA genes; the gene organization, nucleotide composition, and codon usage are consistent with other Heterobranchia species. Notably, comparisons of mitochondrial gene rearrangements indicated that Siphonariidae exhibit extensive and irregular rearrangements within Heterobranchia. Further, we reconstructed the most comprehensive phylogenetic analysis of Gastropoda based on 13 concatenated protein-coding genes. Each subclass of Gastropoda formed a monophyletic clade, with Heterobranchia positioned at the base of the tree, and S. japonica has a sister relationship with S. pectinata. The findings of this study will contribute to a better understanding of the characteristics of the S. japonica mitogenome, provide valuable insights into the phylogenetic relationships within Gastropoda, and underscore the utility of mitochondrial genomes in systematics.