Definition of "water flea" []

• Any of various small aquatic crustaceans of the order Cladocera, especially the daphnid, that typically swim with jerking flealike motions. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.