daphnia(n = noun.animal) water flea - minute freshwater crustacean having a round body enclosed in a transparent shell; moves about like a flea by means of hairy branched antennae;
daphnia, n. any freshwater branchiopod crustacean of the genus Daphnia, enclosed in a transparent carapace and with long antennae and prominent eyes. Also called freshwater flea.
Etymology
mod.L f. Daphne name of a nymph in Gk mythol., f. DAPHNE