Comparative Genomics and Phylogenetic Analysis of the Complete Mitochondrial Genome of Siphonariidae

Siphonariidae is an important family within Tectipleura (Heterobranchia) and is currently the subject of ongoing debate about its morphological classification. Although mitochondria are powerful tools for phylogenetic research, the limited availability of published mitochondrial genome data for species within this family has constrained the improvement of their phylogenetic relationships. To clarify the mitochondrial genome characteristics and phylogenetic status of Siphonariidae, this study included Illumina high-throughput sequencing for the sequencing and analysis of the complete mitochondrial genome of Siphonaria sp. scsio1106 from the Xisha Islands, Hainan, China, and the results were compared with previously published Tectipleura mitogenomes. The mitochondrial genome of Siphonaria sp. scsio1106 is 13,809 base pairs in length and contains 37 genes, indicating an AT bias of 67.06%. The coding region constitutes 97.47% of the genome, indicating a compact structure. The Ka/Ks ratios for the 13 protein-coding genes (PCGs) were less than 1. Phylogenetic analysis based on concatenated 16S rRNA sequences of Tectipleura revealed a close relationship with Siphonaria sp. scsio1106. Divergence time estimation indicated that Siphonariidae diverged from other Tectipleura species approximately 158.6 million years ago (Mya), suggesting that Siphonariidae represents a more recently diverged lineage within Tectipleura. Analysis of gene arrangements revealed three events in the mitochondrial genomes of S. gigas and Siphonaria sp. scsio1106. Our research provides new insights into the evolution of Siphonariidae through phylogenetic analysis, offering valuable data for understanding the evolution and functional organization of mitochondrial genomes within Tectipleura.