A relict or new immigrant? The first record of the planorbid Gyraulus riparius (Westerlund, 1865) in France

A population of a ramshorn snail species new to the French malacofauna, Gyraulus riparius (Westerlund, 1865), has been discovered in the fen surrounding Lake Cerin in southern Jura, eastern France. This population is located more than 450 km south of the previously known localities in Germany, and the species’ status as indigenous to France is therefore discussed. A review of palaeontological data show that the species has been recorded in eastern France during cold periods of the Middle and Lower Pleistocene. Furthermore, Lake Cerin is a small lake of glacial origin, located at an altitude of 766 m a.s.l., with little impact from human activities and inhabited by numerous threatened and protected boreo-alpine species. We postulate that this population indicates a wider past distribution, especially in the south, although we cannot exclude the hypothesis of a more recent introduction (natural or anthropic). We propose that G. riparius should be treated as a species native to France, as defined by the International Union for the Conservation of Nature, and targeted by a conservation and knowledge programme.