The genus Metacyclops is widespread in tropical and temperate regions. Lindberg (1961) established two species-groups within the genus, viz. the minutus-group and the gracilis-group, embracing species characterized by one or two distal spines on the endopodite 3 of leg 4, respectively. At present the genus includes 59 named species and subspecies, 17 recorded in different groundwater habitats.

Mesocyclops is a cosmopolitan and widespread genus found mainly in surface fresh waters, rarely in ground waters. It includes 66 species and subspecies, which are especially common in the tropics and subtropics, a few species also occur in temperate and arctic regions. Taxonomic understanding of the genus has greatly improved during recent years on account of recognition of formerly overlooked microcharacters, such as morphology of the hyaline lamella on the distal segment of the antennula, the presence or absence of spine patterns on the antennular segments, the presence or absence of spines on the maxillular palp, the armature of the intercoxal plate of leg 4, the ornamentation of the spines on the distal segment of the endopodite of leg 4 and the presence or absence of setules on the fifth thoracic segments (Van de Velde, 1984; Dussart & Fernando, 1988; Reid, 1993). Nine species and subpecies are at present known for ground waters.