Animated coloured scanning electron micrograph (SEM) of Water flea (Daphnia sp.). Fresh water cladoceran, Crustacea, Order Cladocera. Daphnia is a genus of small planktonic crustaceans in the order Cladocera. Daphnia species are several small aquatic crustaceans commonly called water fleas (their saltatory swimming style resembles the movements of fleas). Daphnia live in various aquatic environments ranging from acidic swamps to freshwater lakes, ponds, streams and rivers.