The copepods and cladocerans are both groups of the large subphylum Crustacea.
Copepods constitute a class which is widespread in both freshwater and marine environments.
Cladocerans constitute a group of four orders living primarily in freshwater environments. These sources also provide information on sampling, culturing, identification techniques, and include a good review of literature on these groups. The keys for the copepods and cladocerans go only as far as the genus level. To identify zooplankton requires use of a compound microscope. A dissecting microscope is also handy for sorting and counting.