An integrative taxonomic reassessment of the Chinese endemic genus Acuticosta (Bivalvia: Unionidae), with the description of a new genus

Traditional species classification and identification based solely on shell morphology encounter significant challenges in freshwater mussels due to morphological variation and convergence. As a freshwater mussel genus endemic to China, Acuticosta (Bivalvia: Unionidae) has not been systematically revised due to the lack of molecular data. Moreover, the considerable phenotypic variation among individuals further complicates species taxonomy. This study conducted the most comprehensive sampling of Acuticosta to date in China, and the preliminary analyses challenged the monophyly of this genus. Integrating mitochondrial genomics, shell morphology, and soft-body anatomical evidence, we proposed a new genus, Pseudoacuticosta gen. nov., and supported the reclassification of three species originally belonging to Acuticosta: Pseudoacuticosta retiaria gen. & comb. nov., Inversidens trisulcata comb. nov., and Inversidens sichuanica comb. nov. Meanwhile, we identified various phenotypes that complicate species identification in Acuticosta chinensis and Acuticosta ovata, and provided updated DNA barcode data. This study highlights the potential utility of soft-tissue anatomical characteristics for genus-level classification within this taxonomic group. Furthermore, our findings underscore that integrative taxonomy, based on molecular phylogenetics, can effectively resolve issues arising from phenotypic variation and historical classification ambiguities.