DOI: https://doi.org/10.2478/v10058-009-0009-7
The conception of crossed populations in wide practice of taxonomic investigations in Cyclopoida is used for the first time. Applying this conception in taxonomy of cyclopoid copepods we based on revealed facts of the coexistence of sibling species which keep a little morphological hiatus. Hence, next pairs of species we consider as independent ones: Eucyclops speratus (Lilljeborg) and A. serrulatus (Lilljeborg); Paracyclops poppei (Rehberg) and P. fimbriatus (Fischer); Megacyclops latipes (Lowndes), M. viridis (Jurine) and M. gigas (Claus); Diacyclops clandestinus (Kiefer) and D. languidoides (Lilljeborg); D. hypnicola (Gurney) and D. languidoides (Lilljeborg); D. odessanus (Schmankevitsch) and D. bicuspidatus (Claus); Microcyclops rubellus (Lilljeborg) and M. varicans (Sars); Halicyclops septentrionalis (Kiefer) and H. neglectus (Kiefer). Facts of coexistence of Acanthocyclops americanus (Marsh) and its form A. americanus f. spinosa (Monchenko) differing by only one qualitative feature (spine or seta on outer edge on endopodite P4 distal segment) that has no transitive manifestation do not allow us to consider morphological form A. americanus f. spinosa as a separated species from the type A. americanus.