Odabasi, Deniz AnilOdabasi, SerpilErgul, Halim AytekinZilifli, Aytug2025-01-272025-01-2720241869-09632367-0622https://doi.org/10.1127/arch.moll/153/163-168https://hdl.handle.net/20.500.12428/24813This study aims to reveal the freshwater mollusc assemblages from 6 sites sampled along Gonen cayi, a stream which flows into the southern Marmara Sea in north-western Turkiye. The stream was sampled using the multi-habitat sampling method with a hand net. Ten species of freshwater molluscs, most of which are widely distributed in Turkiye, were found in the study area. Among these taxa was an unidentified species of Bithynia, which was only present at 1 site. Its shell and anatomy were compared with other Bithynia species from Turkiye and neighbouring countries and found to differ, which revealed that it is a new species. The discovery of the new species increases the diversity of Bithynia in northern Turkiye to 4 species, and to 11 species for Turkiye. This paper highlights the diversity and endemism of freshwater molluscs in Turkiye and emphasizes the need for further research on the distribution of bithyniid species in the country.eninfo:eu-repo/semantics/closedAccessMolluscafreshwater basinsouthern Marmara SeaTruncatelloideaendemic speciesArticle153216316810.1127/arch.moll/153/163-168N/AWOS:0013471474000012-s2.0-85209139539Q4