Bad taxonomy can kill: molecular reevaluation of Unio mancus Lamarck, 1819 (Bivalvia: Unionidae) and its accepted subspecies

The conservation status of European unionid species rests on the scientific knowledge of the 1980s, before the current revival of taxonomic reappraisals based on molecular characters. The taxonomic status of Unio mancus Lamarck, 1819, superficially similar to Unio pictorum (Linnaeus, 1758) and often synonymized with it, is re-evaluated based on a random sample of major French drainages and a systematic sample of historical type localities. We confirm the validity of U. mancus as a distinct species occurring in France and Spain, where it is structured into three geographical units here ranked as subspecies: U. m. mancus [Atlantic drainages, eastern Pyrenees, Spanish Mediterranean drainages], U. m. turtonii Payraudeau, 1826 [coastal drainages East of the Rhone and Corsica] and U. m. requienii Michaud, 1831 [Seine, Saone-Rhone, and coastal drainages West of the Rhone]. Many populations of Unio mancus have been extirpated during the 20th century and the remaining populations continue to be under pressure; U. mancus satisfies the criteria to be listed as Endangered in the IUCN Red List.