We studied copepods washed off the sponges from two Arctic seas: the Kara and the Laptev. We found new species in families Miraciidae, Canthocamptidae Brady, 1880, Argestidae, and Ectinosomatidae. We describe two new species of the Canthocamptidae Brady, 1880. Heteropsyllus spongiophilus sp. nov. from the Kara Sea, differs from its congeners in the armament of the swimming legs and the maxilliped. Mesopsyllus glacialis sp. nov. from the Laptev Sea, can be distinguished by the legs armament, its sexual dimorphism and the 7-segmented female antennules.

The discovery of a new species of the genus Canthocamptus, C. waldemarschneideri sp. nov., in northern Siberia prompted a taxonomic analysis of this genus. In this work, on the basis of cladistic analysis, we show that the genus is not monophyletic. Based on differences in the structure of the endopods on the second pair of male swimming legs, fifth legs of males and females, and caudal rami, we conclude that the Canthocamptus mirabilis species group is a separate genus, Kikuchicamptus gen. nov. Additionally, two species are transferred to the genus Attheyella, and one species, Canthocamptus gibba, is synonymized. The subgenera Canthocamptus (Baikalocamptus) and Canthocamptus (Canthocamptus) are also synonymized. The new species, Canthocamptus waldemarschneideri sp. nov., is most closely related to the American Canthocamptus assimilis Kiefer, 1931 and differs from it in the ornamentation of the abdominal somites and the shape of the caudal setae.

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A new species of harpacticoid copepod of the family Canthocamptidae, Maraenobiotus supermario sp. nov. is described. The new species was found in interstitial waters of the moss tundra of the Lena River Delta, Siberia. This species belongs to the vejdovskyi-species group. The new species differs from its congeners in the apical caudal setae lacking a bulbous proximal part, and in the unique structure of the mandibular palp with only one seta. We also present detailed figures and description of sensilla and pores on the somites surface, which could be used in the future to diagnose and solve taxonomic issues of this complex genus.

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.