The water fleas belong within the crustacean class Branchiopoda but there is considerable debate concerning the higher classification of the class (see Fryer, 1987). The taxon Cladocera may not be monophyletic, representing instead a level of organisation within the diplostracan branchiopods. Most cladocerans are freshwater but a few, mainly belonging to the infraorder Onychopoda, are marine or occur in brackish waters, such as the Baltic Sea. The data are compiled from Rammner (1939) and Alonso (1996).
- Alonso, M. 1996. Crustacea Branchiopoda. In, Fauna Iberica, Museo Nacional de Ciencias Naturales (CSIC), Madrid, 7: 486pp.
- Fryer, G. 1987. A new classification of the branchiopod Crustcea. Zool. J.Linn. Soc. 91: 357-383.
- Rammner, W. 1939. Cladocera. Fiches D’Identification du Zooplankton. Conseil International pour l’Exploration de la Mer, Sheet 3. 4pp.