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a genus of freshwater animals of the suborder Cladocera. Daphnia measure 1–3 mm and have a transparent, oval, chitinous shell, whose valves are united on the dorsal side and open in the form of slits on the ventral side. Daphnia are dioecious. Some summer generations are represented only by females, which reproduce parthenogenetically. In the fall, males also appear; fertilization occurs, the females deposit one or two fertilized eggs, which are covered with a thick membrane. These eggs hibernate; in the spring females develop from them. There are a total of 26 species, 14 in the USSR; they are distributed everywhere, except in polar regions. Daphnia live in lakes, ponds, temporary bodies of water, and the backwaters of slow-moving rivers. They feed on bacteria, unicellular algae, protozoans, and the smallest particles of plant detritus. Daphnia serve as food for recently hatched and young fish (they are raised for this purpose in fisheries). Daphnia are intermediate hosts of some worms that in their adult form parasitize various vertebrates, including domestic ducks.