The freshwater fauna of nine caves in central Abkhazia, western Caucasus, revealed 35 species of stygobionts, including 15 new species to be described elsewhere. The number of species per station increased from the depth towards the entrance in caves Golova Otapa and Abrskila, becoming the highest in the epigean part. In both caves, two abundance peaks of aquatic invertebrates were registered: one in the entrance area, associated with the development of amphibiotic insect larvae, the other in the depths due to the high numbers of stygobionts. In Cave New Athos, the highest species richness and abundance were observed in large lakes. In caves Golova Otapa and Abrskila, two faunistic complexes with complementary distributions were found, the first due to amphibiotic insects in the cave entrance area, the second one composed of stygobionts in the deep areas. The impact of anthropogenic factors on aquatic cave communities was also noted. The stygobiotic faunas of all caves studied were clearly divided into three groups, following the number of river valleys in which they were situated. The stygobiont faunas of the caves located within one river valley appeared to be 50% similar. In contrast, the fauna composition of the stygobionts from caves situated in different valleys shared not more than 12% species in common. Stygobiotic shrimps and gastropod mollusks show profound local endemism. Stygobiotic Amphipoda penetrating the ground waters revealed wide distributions between cave systems within a single karst massif.

The Putorana Plateau (Krasnoyarsk Territory, Russia) is one of the largest mountainous regions of subarctic Eurasia. Studies of aquatic ecosystems of this are far from complete. In particular, microcrustaceans (Cladocera и Copepoda) of the Putorana Plateau are poorly investigated, although they are one of the main components of meiobenthic and zooplanktonic communities and a target for monitoring of the anthropogenic influence and climate change. An open question is a biogeographical status of the crustacean fauna of the plateau. Additionally, it is unknown which environmental factors significantly affect benthic and planktonic crustacean assemblages? Based on the samples collected in tundra and forest tundra ponds in the western and central parts of the plateau, analysis of the composition of crustacean fauna and factors regulating the assemblage structure was performed. In total, 36 Cladocera and 24 Copepoda species were found. Of these, 23 taxa are new for the region, and four are new to science. Species richness of Copepoda is higher in the central part and on the western slopes of the plateau than in foothills, while number of the Cladocera species in contrast decreases in mountainous areas. Variations in meiobenthic assemblages are due to the research area, type of water supply and less affected by altitude above sea level. For planktonic assemblages the size of the water body and, to a lesser degree, by macrophytes species composition was significant. Almost 12.8% of microcrustacean species of the Putorana Plateau can be attributed to glacial relics. Crustacean fauna of the Putorana Plateau has a high species richness and distinguishes significantly from the fauna of both western and eastern regions of the Arctic. The specifics of faunal composition of the region are connected to the climatic features of Middle Siberia and the retaining of the Pleistocene fauna in some glacial refugia.

Eucyclops speratus (Lilljeborg, 1901) (Copepoda, Cyclopoida, Cyclopidae) was studied using various methods. Molecular genetic methods (comparison of COI and ITSn molecular markers) have shown that this species represents a species complex, and the following methods were used to search for differences between the species: analysis of qualitative and quantitative characters, linear morphometrics, landmark-based geometric morphometrics, and integumental pore pattern of the cephalothorax. Eucyclops sibiricussp. nov. from Middle Siberia is described. The two studied species can be considered pseudocryptic; the main morphological difference between the species is the number of setules on the inner side of the first and second exopod segments of the fourth pair of swimming legs: E. sibiricussp. nov. has 6–10 and 7–17 setules, respectively; E. speratus has 0–3 and 0–6 setules, respectively. The morphometry and integumental pore pattern of the cephalothorax were ineffective for identification and separation of species. The existing previous records of E. speratus were also analyzed, and the records of this species in the Irkutsk region (Russia), as well as in Japan and Korea, are attributed to E. sibiricussp. nov.

A new species, Diacyclops dyabdar sp. nov. from the Diacyclops crassicaudis (Sars, 1863) species group from northern Middle Siberia, is described. This species is interesting from an ecological point of view, as it lives mainly in watercourses. It is well-distinguished from other species of the group by the presence of spinules on the first segments of the third and fourth pairs of swimming legs, details of the ornamentation on the fourth pair of legs and caudal rami. A detailed comparison of the new species and D. crassicaudis is presented. Molecular markers, including cytochrome c oxidase (COI) of mtDNA and 18S rRNA, ITS1 and ITS2 of nuclear DNA were obtained for a single female of D. dyabdar sp. nov. A morphometric analysis of species and subspecies of the D. crassicaudis group was carried out. It showed slight differences between the described subspecies and some species. On this basis, the subspecies D. crassicaudis, as well as D. iranicus Pesce & Maggi, 1982 and D. fontinalis Naidenow, 1969, are synonymized with the subspecies type. A more precise diagnosis of the D. crassicaudis group is indicated. This group now includes six species. The taxonomic position of several questionable taxa of Diacyclops Kiefer, 1927 described from Iran is discussed: D. landei Mahoon & Zia, 1985; D. bicuspidatus jurenei Najam-un-Nisa, Mahoon & Irfan Khan, 1987; D. landei richardi Parveen, Mahoon & Saleem, 1988 and D. jurenei Parveen, Mahoon & Saleem, 1988. These taxa are accepted as nomen dubium.