 daphnia is a genus of small, planktonic crustaceans,  in length. daphnia are members of the order cladocera, and are one of the several small aquatic crustaceans commonly called water fleas because 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. the two most readily available species of daphnia are d.&nbsp;pulex (small and most common) and d.&nbsp;magna (large). they are often associated with a related genus in the order cladocera: moina, which is in the moinidae family instead of daphniidae and is much smaller than d.&nbsp;pulex (approximately half the maximum length). daphnia eggs for sale are generally enclosed in ephippia (a thick shell, consisting of two chitinous plates, that encloses and protects the winter eggs of a cladoceran). == appearance and characteristics == thumb|left|the beating heart of daphnia under the microscope the body of daphnia is usually  long, and is divided into segments, although this division is not visible.{{cite web |url=http://www.seagrant.sunysb.edu/oli/olei-daphnia.htm |title
Branchiopoda Fishkeeping Freshwater_crustaceans