'Water flea' definitions:

Definition of 'water flea'

From: WordNet
noun
Minute free-swimming freshwater copepod having a large median eye and pear-shaped body and long antennae used in swimming; important in some food chains and as intermediate hosts of parasitic worms that affect man e.g. Guinea worms [syn: cyclops, water flea]
noun
Minute freshwater crustacean having a round body enclosed in a transparent shell; moves about like a flea by means of hairy branched antennae [syn: daphnia, water flea]

Definition of 'Water flea'

From: GCIDE
  • Water flea \Wa"ter flea`\ (Zool.) Any one of numerous species of small aquatic Entomostraca belonging to the genera Cyclops, Daphnia, etc; -- so called because they swim with sudden leaps, or starts. [1913 Webster]