ABSTRACT
Cladocera were long thought to be a group in which a few species had widespread, sometimes almost ubiquitous distributions. Recent taxonomic revisions in the group reveal that the contrary is probably the case, i.e. this is a group in which discretely defined members of closely related species have rather restricted distributions. Cladocerans are probably a very old group whose origins go back to an originally ubiquitous fauna rather uniformly distributed on the supercontinent of Pangaea. Consideration of ability to hybridize and time of gamogenesis can offer some insights into sorting out the biogeographic and ecologic histories of specific cladoceran taxa.
