Bythotrephes arcticus, Lilljeborg, 1901

Korovchinsky, Nikolai M., 2019, Morphological assessment of the North Eurasian interspecific hybrid forms of the genus Bythotrephes Leydig, 1860 (Crustacea: Cladocera: Cercopagididae), Zootaxa 4550 (3), pp. 340-356 : 346

Hybrid form Bythotrephes arcticus x Bythotrephes cederströmii

In samples from the delta of the river Severnaya Dvina (north of European Russia), Litvinchuk (2002: P. 85, Fig. 15, 2007) found, among many individuals of B. arcticus (syn. B. crassicaudus Lilljeborg ), one adult female of the interspecific hybrid which she named “ B. cederströmii x B. crassicaudus ”.

Diagnosis. It has general body structure similar to that of B. arcticus Lilljeborg : massive body with length 3.9 mm, comparatively short thoracic limbs of the first pair (tl I), with long apical setae on their two proximal endopodital segments, and comparatively short and basally thick caudal process. The postabdominal and caudal claws are larger than usual in this species and curved not backwards but either slightly forward or down. The caudal process is slightly bent near its middle part, bearing groups of small dorsal and ventral denticles.

Litvinchuk (2002) reported two other specimens of the hybrid form from two Siberian lakes (Krasnoyarsky Region) but these records have not been documented.