Diacyclops cohabitatus Monchenko 1980 known only from the groundwater of the Carpathian mountains in Ukraine is redescribedfrom specimens collected in the Danube alluvial plain, the Lobau, at Vienna. In this area two stygobiont species belongingto the D. languidoides - group co-occur as well. D. cohabitatus can be differentiated from these latter Diacyclops specieson the basis of several morphological traits of antennae, P4 and caudal rami. Its relationship with other members of the D. languidoides- group (e.g. D. languidoides goticus) is discussed.