A New Record and Three Redescriptions of Rissoinidae from China’s Hainan Island, with the First Presentation of Two Mitochondrial Genomes in the Family Rissoinidae

The family Rissoinidae represents a significant component of microgastropod diversity, with a global distribution spanning temperate to tropical zones and encompassing over 300 recorded species. Hainan Island, the largest island in the South China Sea, harbors a rich diversity of mollusks, but the family Rissoinidae remains poorly studied in this region. Here, we report three rissoinid species and one newly recorded species from Hainan Island, providing detailed taxonomic descriptions supported by SEM imaging. For the first time, we provide the mitochondrial genomes of Rissoina cardinalis and Phosinella seguenziana, analyzing their genome structure and nucleotide composition, thereby addressing the existing knowledge gap in Rissoinidae research. A phylogenetic tree of the family Rissoinidae was reconstructed using the COI gene, clarifying the intergeneric relationships within the family. Notably, the genus Rissoina is revealed as a non-monophyletic group, likely due to the limitations of single-gene analyses in providing adequate phylogenetic information.