The Pond Snails of the Genus Radix (Gastropoda, Lymnaeidae) in Issyk-Kul Lake (Central Asia), with a Review of Radix in Ancient Tectonic Lakes of the World

Lake Issyk-Kul, situated in the Republic of Kyrgyzstan, is one of the largest lakes in Central Asia. Though this brackish-water basin holds only a species-poor fauna of molluscs, the number of species inhabiting Issyk-Kul and their true taxonomic position remain unsatisfactorily studied. Most nominal species of Mollusca reported from Issyk-Kul are known from empty shells only and have never been studied molecularly. This study reports the results of a revision of the genus Radix (Gastropoda:Hygrophila:Lymnaeidae) based on the integrated approach. We revealed that only two species of this genus inhabit Issyk-Kul Lake: Radix auricularia (Linnaeus, 1758) and R. obliquata (von Martens, 1864). The former species is widespread in the Palearctic and has an enormous range, whereas the latter is considered here to be endemic to Issyk-Kul Lake. All records of R. obliquata from waterbodies other than Issyk-Kul Lake are, most probably, based on misidentification. To date, no molecular evidence of the presence of R. obliquata outside Issyk-Kyl is available. The third species of Radix discussed in this paper, R. subdisjuncta (Nevill, 1878) sensu Kruglov and Starobogatov, 1993, is identical to R. obliquata and represents, most probably, an ecological morph ("race") of the latter. The paper provides a review of Radix species recorded in other ancient tectonic lakes of the world (Baikal, Victoria, Ohrid, etc.). Though the lymnaeid snails are generally scarce in such lakes, the genus Radix represents an exception, with several species being endemics of various tectonic lakes (Issyk-Kul, Lugu, Skadar, Trichonis, and Biwa).