A new gastropod species, Pseudobaikalia michelae Sitnikoiva & Kovalenkova, sp. n., (family Baicaliidae) is described from Lake Baikal. This is the first new species from the Baicaliidae for forty years. The new species is distinguished from its sister taxa by means of comparative morphology as well as analyses of DNA sequences (mtDNA and an intron of alpha-subunit gene of ATP-synthase). It was found in the southern and central-eastern parts of the lake where it occurs sympatrically with three other baicaliid species. Characters of the female reproductive system (i.e., a long oviduct loop with 2-3 narrow tube-like evaginations) and the aperture (i.e., oval shape with a simple outer lip) place these snails in the genus Pseudobaikalia Lindholm, 1909. The new species is most similar in its shell morphology to the northern Baikal species Pseudobaikalia jentteriana (smooth elongated shape) but differs by a more oval aperture that is slightly angled to the columella. Combined mitochondrial and nuclear sequences in a Bayesian analysis showed that all specimens of Pseudobaikalia michelae sp. n. form a well-supported clade.
Keywords: Gastropoda; Lake Baikal; Pseudobaikalia michelae; Siberia; new species.