Аннотация:tThe study addresses an uneven and incomplete understanding of copepod fauna in Middle Siberia,particularly in its northeastern region. While the microcrustacean composition in the Lena River Del-ta is well documented, the Tiksi settlement vicinity, nearby the Lena Delta, remains unexplored. Thisresearch focuses on characterizing copepod crustaceans in Tiksi's waters. The collected data enrichesthe microcrustacean distribution database in Arctic and Subarctic regions worldwide and facilitatesan analysis of copepod faunal variation in northeastern Eurasia. A total of 64 copepod species werediscovered near Tiksi, with 19 being newly identified for the region. Brackish water reservoirs andlakes demonstrated the greatest diversity within the fauna. The structure of copepod species complexeswas consistent among water bodies of the same hydrological type. In brackish lagoons, bays, and lakes,species complexes exhibited intricate, multilevel functional and trophic structures. In contrast, riversand streams displayed simplified complex structures. Around 20% of the examined fauna displayedEast Asian-North American ranges, suggesting a connection to the ancient land of Beringia. Similar-ity among local Copepoda orders' faunas is linked to crustaceans' dispersal ability, with increasingsimilarity from Harpacticoida to Calanoida and Cyclopoida. Two distinct groups of regions with com-parable faunas are recognized in northeastern Eurasia: European-Siberian, divided into European and Siberian branches, and Far Eastern. The potential existence of transitional zones between these groupsis also discussed.
