Complete mitochondrial genomes of Sinonovacula rivularis and Novaculina chinensis and their phylogenetic relationships within family Pharidae

Pharidae is one of the most ecologically and commercially significant families of marine Bivalvia; however, the taxonomy and phylogeny of Pharidae has been ongoing for quite some time and remains a contentious issue. Here, to resolve some problematical relationships among this family, the complete mitochondrial genomes (mitogenomes) of <i>Sinonovacularivularis</i> (17,159 bp) and <i>Novaculinachinensis</i> (15,957 bp) were assembled, and a comparative mitochondrial genomic analysis was conducted. Both mitogenomes contain 12 protein-coding genes, 22 transfer RNA genes, and two ribosomal RNA genes. Among the published Pharidae mitogenomes, <i>N.chinensis</i> exhibited the smallest genome size but the highest AT content. The results of the phylogenetic trees confirmed the monophyly of the family Solenoidea, and indicated that <i>N.chinensis</i> and <i>Sinonovacula</i> (<i>S.constricta</i> and <i>S.rivularis</i>) were closely related in the family Pharidae. From the CREx analysis, we found that transposition and tandem duplication random losses (TDRLs) might have occurred between Pharidae and Solenidae. Moreover, positive selection was detected in nad5 of the foreground <i>N.chinensis</i>, and divergent evolution occurred at site 144 in the freshwater and marine lineages. Overall, our findings provide new molecular data on the phylogenetic and evolutionary relationships of Pharidae, and contribute to unraveling the salinity adaptations of Pharidae.