Historical species richness of Semisulcospira (Caenogastropoda: Semisulcospiridae) in former water bodies of the Lake Biwa system, Japan

Investigation of museum specimens plays an important role in explaining the loss of biodiversity and historical environmental changes. The Lake Biwa system, in central Japan, has undergone significant environmental changes, resulting from the reclamation of Oguraike Pond and the construction of Lake Biwa Canal. Despite anthropogenic changes to the Lake Biwa system, impacts on freshwater molluscs remain largely unknown. In this study, 46 specimens preserved at four Japanese museums and 45 previous occurrence records of the genus Semisulcospira (Gastropoda: Semisulcospiridae), obtained from these water bodies, were re-identified based on their shell morphology. Four and nine species were re-discovered in Oguraike Pond and in Lake Biwa Canal, respectively. Of these, S. kurodai was recorded from the pond for the first time; S. davisi, S. decipiens and S. elongata were also newly identified in the canal. These records clarify the past distribution of Semisulcospira species in the lower reaches of the Lake Biwa system, indicating the importance of the study areas for freshwater molluscs. The observed historical transition in species composition and occurrence patterns is useful for species delimitation and habitat estimation of the genus and may also contribute to future ecological and taxonomic studies.