The first record of Chironomusnuditarsis Keyl, 1961 from Sevan Lake (Armenia) confirmed by morphology, karyotype and COI gene sequence.

Chironomusnuditarsis Keyl, 1961 is recorded from Sevan Lake for the first time. This species is widespread in Europe, the Caucasus, and Siberia. For species identification, we used a comprehensive approach that included morphological, cytogenetic and molecular genetic analyses. Morphological analysis showed a high similarity with the description. Nine chromosome banding sequences ndtA1, ndtA2, ndtB2, ndtC1, ndtD1, ndtE1, ndtF1, ndtG1, and ndtG2 were found. The banding sequences ndtA1, ndtA2, ndtG1, and ndtG2 are species-specific for C.nuditarsis and allow us to accurately distinguish it from the sibling species Ch.curabilis Belyanina, Sigareva et Loginova, 1990. Molecular-genetic analysis of the COI gene sequences has shown low genetic distances of 0.38-0.95% in the sibling species Ch.nuditarsis and Ch.curabilis complex and the insufficiency of using a single COI as a molecular marker for their separation.