Description of two new species of the genus Trochus Linnaeus, 1758 (Gastropoda, Trochidae) from the South China Sea

Two new species of the gastropod family Trochidae, <i>Trochus nanhai</i> <b>sp. nov.</b> and <i>Trochus parvus</i> <b>sp. nov.</b>, are described from the South China Sea. Morphological comparisons and species delimitation analyses based on molecular phylogeny support the distinctiveness of the two species. <i>Trochus nanhai</i> <b>sp. nov.</b> exhibits substantial variation in shell morphology, which increases the difficulty of morphological characterization. Nevertheless, it can be distinguished by diagnostic characters such as the presence and arrangement of pustules along the suture of each whorl. Additionally, multiple species delimitation methods (ASAP, ABGD, bPTP and GMYC) revealed potential taxonomic inconsistencies within previously identified <i>Trochus</i> species. To assist visualization and facilitate future taxonomic studies, we applied 3D modeling techniques and extracted geometric morphometric parameters of two new species. Detailed morphological descriptions, diagnostic characters, illustrations, and 3D models are provided. This study enhances our understanding of <i>Trochus</i> diversity and taxonomy.