Daphnia (or Daphnids) are members of a collection of animals that are broadly termed as “water fleas”. These are predominantly small crustaceans, and Daphnia belong to a group known as the Daphniidae (which in turn is part of the Cladocera, relatives of the freshwater shrimp, Gammarus et al, and the brine shrimp, Artemia spp). They get their common name from their jerky movement through the water.
It is important to distinguish between Daphnia and other “water fleas” such as the various species of copepod (like Cyclops spp) and ostracod (Cypridopsis et al) which do not directly come under the scope of this document, but share many of the feeding habits of Daphnids. The jerky movement, general shape (and, to a lesser extent, colour) of daphnia are the best way to distinguish them without magnification.