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Two new species of the genus Parachironomus Lenz, P. aquilonis sp. n. from the northern Urals and P. khatyrka sp. n. from the Russian Far East, are described and figured based on the morphology of the adult males. Adult males of P. hazelriggi Spies, 2000 and P. subalpinus (Goetghebuer, 1931) are redescribed and illustrated; both species are recorded for the first time from Russia, P. hazelriggi is new for the Palaearctic region.

A long-term study implemented in the Amur River basin enabled us to generate an updated checklist of 606 valid species in Chironomidae (Diptera) which are composed of 129 genera and six subfamilies, with 98 (17%) described new species belonging to 46 genera. Among the 98 recently described species, 46 ones (45%), were considered as possible endemics and sub-endemics. The numbers of species and genera by subfamilies is as follows: Podonominae (3 species; 3 genera), Tanypodinae (17; 9), Diamesinae (25; 11), Prodiamesinae (7; 3), Orthocladiinae (307; 57) and Chironominae (247; 46). The higher numbers of species (421 and 410, respectively) were recorded in the Lower and Middle parts of the Amur River basin, as compared with the Upper part of the basin. Most of the recorded chironomids (387 species, 67%) are Palaearctic in distribution, while others (191, 33%) are widely Holarctic. Species with Palaearctic distribution mostly have the following range types: East Palaearctic continental (23%); East Palaearctic continental-insular (20%); Palaearctic transpalaearctic (14%); Palaearctic amphi-Eurasian (10%).

An illustrated morphological description of the adult males of Tanytarsus heliomesonyctios Langton, 1999, is provided for the first time. The males were found in mountain lakes Bolshoi Darpir (Momsky District of the Republic of Sakha (Yakutia)) and Momontai (Susumansky District of the Magadan Region), located in the Kolyma River basin. Females, pupae and larvae of T. heliomesonyctios was previously described from Spitsbergen, Jan Mayen (Norway) and Ellesmere Island (Arctic Canada), and considered parthenogenetic. Tanytarsus heliomesonyctios is here for the first time noted for the fauna of Russia. Comparison of DNA barcodes shows high K2P nucleotide distances (1.7%) between the sexual populations (Norway and Russia) and the parthenogenetic populations (Svalbard and Canada). In the Bayesian tree, the COI- sequences from adult males group as sister to a strongly supported clade of sequences from parthenogenetic populations. This apparently indicates a single origin of parthenogeneticity, perhaps due to extreme environmental conditions.