Alien Gastropods among Endemics in Open Areas of Lake Baikal

Until the middle of the last century, Palearctic–Siberian gastropod fauna inhabited the inlets of large bays and sors of Lake Baikal, which are similar to Siberian water bodies in the environment. The endemic species occupied open areas of the lake with cold water, heavy storms, and other specific ecological conditions. Based on analysis of the morpho-anatomical traits and genetic distances by the COI mtDNA gene fragment, five alien species were detected in open regions of Baikal. In addition to the previously found Radix auricularia (Linnaeus 1758), we found out the habitation of 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). Based on the materials of expeditions in 1993–2023, we present photographs of the shells of alien species, reproductive organs for some of them, a schematic map of their records in the open Baikal, as well as information on coexisting endemic species of gastropods. Albinos among R. auricularia and several snails with a rudimentary copulatory organ among R. cf. zazurniensis were found. Potential reasons for the penetration of alien species into the open Baikal regions are discussed.