Cladocerans are essentially freshwater organisms, many of which have been able to penetrate slightly saline waters (up to 5% salinity), both thalassic and athalassic, some of which occur at higher salinities, and a few of which, mostly non-chydorids, penetrate still higher salinities (15—30% and even higher) and may be confined to these salinities. Three previous studies from Saskatchewan, Iran, and Germany (the latter including thalassic waters) have been analyzed, and records for the athalassic saline waters of the World have been summarized; all results show a decline, at some point, in species number against increasing concentration of salinity.