Redécouverte de la Bythinelle d'Amance, Bythinella cylindracea (Paladilhe, 1869) (Gastropoda, Caenogastropoda, Bythinellidae) dans sa localité type (Amance, Aube, Région Grand Est, France)

Extended abstract ̶ The genus Bythinella Moquin-Tandon, 1856, is one of the most species-rich genus of European hydrobioid gastropods, with almost 140 valid species, of which 49 have been recorded in France. These small aquatic snails, typically found in springs and associated habitats, show some morphological variability, which makes species delimitation difficult. This short note reports on the recent rediscovery of Bythinella cylindracea (Paladilhe, 1869), the so-called "Bythinelle d'Amance", in the department of Aube (north-eastern France). The specimens attributed to B. cylindracea were collected between 2021 and 2024 from several localities in Aube, including the type locality of Amance. New and old records allow a preliminary estimate of the distribution of the species, which is estimated to be around 600 km². The shells observed are conical and elongated, with a characteristic axial ridge behind the aperture, as originally described by Paladilhe.To date, the taxonomic validity of B. cylindracea has not been assessed using integrative approaches combining molecular and anatomical data. However, for the time being, the rediscovery of topotypic specimens allows the name to be applied unambiguously to closely geographic populations. These specimens can serve as a taxonomic reference point, allowing comparisons between populations, for example with nominal taxa historically described from the Aube, currently considered junior synonyms of B. cylindracea [Belgrandia lanceolata Locard, 1893; Belgrandia riparia Locard, 1893; Belgrandia sequanica Paladilhe, 1870; Belgrandia tricassina Locard, 1893; Bythinella bourguignati Locard, 1893], or with B. geisserti, for example, a close morphological and geographic species.While the species validity of B. cylindracea remains to be tested with integrative evidence, the availability of newly collected topotypic individuals paves the way for future studies. These specimens will facilitate the taxonomic calibration of forthcoming molecular and morphological analyses. In the meantime, B. cylindracea should be provisionally considered as a distinct French endemic with a narrow range. We encourage naturalists and malacologists to document similar populations in north-eastern France to better understand the diversity and distribution of this nominal species.