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Study of the external morphology of Leptodora kindtii Focke, 1844 (Crustacea: Branchiopoda: Haplopoda), with notes on its relation to Cladocera and on conspecificity of populations of the species over the Eurasian range

Leptodora kindtii is a peculiar carnivorous crustacean widely distributed and occupying a prominent position in the freshwater planktonic communities. This species was originally found and described in the 1840–1860s and since then it has been a subject of numerous studies, morphological, embryological, behavioural, and ecological, which elucidated various aspects of its body structure and mode of life. Nevertheless, analysis of the literature and personal investigation of material on the species have led to the conclusion that the morphology of the species was not studied properly and the previous data might be incorrect and inconsistent, which obstructed proper understanding of its phylogeny, taxonomic position, and habits. In the present investigation, the external morphology of L. kindtii is described and analysed in detail, from comparative morphological and eco‐morphological aspects. Also, the morphological features of representatives of the species from different populations over the vast area of its Eurasian range have been studied with respect to their intra‐ and interpopulational variability and taxonomic significance. It has been shown that the majority of populations of L. kindtii from Europe to the Far East of Russia do not display any significant morphological differences, which testifies to their conspecificity. Only a small set of adult specimens from Lake Bolon (the Amur River basin, Far East of Russia) differed considerably from others in their small size and body proportions which implies the occurrence of another species of the genus in this region to be studied and validated in the future together with the enigmatic cave species L. pellucida Josef. In spite of high morphological peculiarity, L. kindtii possesses a number of “core” characteristics, which undoubtedly show its close relationship with other mostly small branchiopods (Ctenopoda, Anomopoda, Onychopoda) traditionally united in the taxon Cladocera whose validity has also been supported by modern molecular‐genetic studies.