The distribution of chydorid Cladocera in Canada

The distribution of chydorid Cladocera in Canada is given based on the examination of 584 samples collected from all the provinces and territories from 1978 through to 1984. Some species show regional distributions, while others are widely distributed. The preferences shown by some species to particular substrates are discussed. Further evidence is presented to show that some taxa previously claimed to be conspecific in Europe and North America may be different. In some instances the adult males tend to be more highly differentiated than the females, particularly in the structure of the postabdomen. The importance of taxonomic and distributional studies in understanding the biogeography of North American chydorids is discussed.