water flea

noun

any of various small crustaceans that move about in the water like fleas, as those of the genus Daphnia.

Origin

1575-85

Examples from the web for water flea

Add the humble water flea, a freshwater relative of shrimp, to the list of creature with their genes mapped.
When a water flea or some other small creature swims past, it bends trigger hairs on the bladder, causing a flap to open.
Small animals such as the spiny water flea can travel unnoticed by hopping onto a kayak or other recreational equipment.

British Dictionary definitions for water flea

noun

any of numerous minute freshwater branchiopod crustaceans of the order Cladocera, which swim by means of hairy branched antennae See also daphnia