An integrative approach to the delimitation of pseudocryptic species in the Eucyclops speratus complex (Copepoda, Cyclopoida) with a description of a new species

<i>Eucyclopssperatus</i> (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. <i>Eucyclopssibiricus</i> <b>sp. nov.</b> 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: <i>E.sibiricus</i> <b>sp. nov.</b> has 6-10 and 7-17 setules, respectively; <i>E.speratus</i> 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 <i>E.speratus</i> were also analyzed, and the records of this species in the Irkutsk region (Russia), as well as in Japan and Korea, are attributed to <i>E.sibiricus</i> <b>sp. nov.</b>