Comparative Genomic and Mitochondrial Phylogenetic Relationships of Ovulidae (Mollusca: Gastropoda) Along the Chinese Coast

The family Ovulidae, closely related to Cypraeidae (cowries), comprises approximately 260-280 species predominantly inhabiting tropical and subtropical shallow marine environments. Unlike cowries, ovulids have a more specialized diet, with most species feeding on soft corals, leather corals, or black corals. Given their proximity in distribution and close phylogenetic relationship, dietary specialization may have played a crucial role in the evolutionary divergence of cowries and ovulids. However, unlike cowries, the traditional morphological classification of Ovulidae has proven challenging due to substantial variability influenced by their host organisms, leading to ongoing debates regarding species delimitation and taxonomy. In this study, we collected 15 Ovulidae species from China's offshore waters, including the first regional record of <i>Habuprionovolva aenigma</i> (M. Azuma & C. N. Cate, 1971). We successfully obtained mitochondrial genomes for 14 of these species and found that, with the exception of <i>H. aenigma</i>, they exhibit the typical mitochondrial genome structure of Caenogastropoda. Our phylogenetic analyses based on mitochondrial genome data, along with the discovery of a unique mitochondrial tRNA gene order in the subfamily Prionovolvinae, support recent studies suggesting that the genera <i>Naviculavolva</i> and <i>Contrasimnia</i> should be reclassified from the Simniinae to the Prionovolvinae. Additionally, our results do not support the monophyly of the genus <i>Cuspivolva</i>. Furthermore, our findings indicate that mitochondrial gene rearrangements occurred after the divergence of the subfamilies Prionovolvinae and Ovulinae. Additionally, we found that Ovulidae species display significantly higher Ka/Ks ratios compared to Cypraeidae, indicating different selective pressures, possibly linked to their unique feeding habits. This research enhances the understanding of Ovulidae phylogeny and provides genomic resources for future studies.