Characterization of the Complete Mitochondrial Genome of Angulyagra polyzonata and Its Phylogenetic Status in Viviparidae.

Angulyagra polyzonata is an economically important mollusk in China, but detailed insights into its mitochondrial genome remain scarce. In this study, we sequenced and comprehensively analyzed the structural features and selection pressures of the A. polyzonata mitochondrial genome. The maximum likelihood method and Bayesian phylogenetic inference method were used to construct a phylogenetic tree of A. polyzonata with 21 other species, including gastropods and bivalves. The full-length mitochondrial genome of 17,379 bp was found to include 22 transfer RNA genes, 2 ribosomal RNA genes, and 13 protein-coding genes, exhibiting similarity to the composition and arrangement of mitochondrial genes in other gastropod species. Notably, the Ka/Ks ratios of mitochondrial protein-coding genes (nad5, cox3, nad3, nad2, cox1, cox2, atp8, atp6, nadl, nad6, cob, nad4l, and nad4) were <1, which indicates that the snail genes of the three genera of the family may have been subjected to strong natural selection pressure during the evolutionary process, so that the number of synonymous mutations (ks) in genes was much more than that of nonsynonymous mutations (ka). Comparative genomic analysis indicated that, apart from the absence of trnW and trnQ, the gene composition of A. polyzonata shares a high degree of homology with other members of the conical snail family. Phylogenetic analysis demonstrated that the selected species could be classified into two primary clades in which A. polyzonata clustered with the Viviparidae family. This study bridges the knowledge gap regarding the mitochondrial genome of A. polyzonata and offers valuable insights into the systematic relationships within the Viviparidae family.