Taxonomic reassessment of Scabies (Bivalvia: Unionidae) species in China based on multilocus and mitogenomic phylogenetic analyses.

Effective species conservation necessitates the ability to accurately differentiate among species, a challenge compounded by taxonomic uncertainties in freshwater mussels due to substantial intraspecific variation and pronounced phenotypic plasticity in shell morphology. The taxonomic status and species validity of Scabies longata and S. chinensis, two species endemic in China, have been under continuous debate since establishment. The lack of essential molecular data required for a comprehensive systematic study has resulted in the unresolved taxonomic status of these two species. This study presents molecular data, including COI barcoding, COI + 28S rRNA, and mitogenomic data combined with morphological characteristics to assess the validity of S. longata and S. chinensis. Both morphological and COI barcoding data support the conclusion that S. longata and S. chinensis are junior synonyms of Nodularia douglasiae and N. nuxpersicae respectively. Our findings suggest the absence of Scabies species in China. Mitochondrial phylogenetic analyses were used to further elucidate intrageneric relationships within the genus Nodularia, revealing the following relationships: (N. breviconcha (Nodularia sp. 1 (N. douglasiae (N. nuxpersicae, N. nipponensis)))). We underscore the significance of employing an integrated taxonomic approach for species identification, especially given the considerable morphological disparities between larvae and adult freshwater mussels. Proper morphological identification of adult specimens is essential for extracting meaningful taxonomic characters. Furthermore, our findings suggest a notable resemblance between the freshwater bivalve fauna in southern China and those east of the Mekong River. ZooBank: urn:lsid:zoobank.org:pub:DA87D330-5E23-4F4B-8CC2-CBA3CD191BE8.