Alien gastropods among endemics in the open waters of Lake Baikal

Until the middle of the last century, the Palearctic-Siberian gastropod fauna that inhabited the ‘sors’ and small coves of the larger bays of Lake Baikal was similar in environmental factors to Siberian water-bodies. Endemic species occupied open areas of the lake, with cold water, strong storms, and other specific environmental conditions. Based on morpho-anatomical characters and genetic distances of the COI mtDNA gene fragment between related species, five alien species were identified from open Baikal waters. In addition to the previously found Radix auricularia (Linnaeus, 1758), there were Radix cf. zazurniensis (Mozley 1934) (Lymnaeidae), Cincinna sorensis (Dybowski 1886) and C. cf. korotnevi Lindholm 1909 (Valvatidae), as well as Gyraulus cf. acronicus (Férussac 1807) (Planorbidae). A schematic map of the records of the alien species in the open littoral of the lake is presented, based on material taken by expeditions carried out in 1993–2023, as well as photographs of the shells and reproductive organs for some of the alien species, and information on coexisting endemic species of gastropods are given. We found albino individuals among R. auricularia and a few snails of R. cf. zazurniensis with afallic copulatory organs. Possible reasons for the invasion of the alien species and possible invaders into the open waters of Baikal are discussed.