Source : Webster's Revised Unabridged Dictionary (1913)

Daphnia \Daph"ni*a\, n. [NL.] (Zo["o]l.)
   A genus of the genus {Daphnia}.

Source : WordNet®

daphnia
     n : minute freshwater crustacean having a round body enclosed in
         a transparent shell; moves about like a flea by means of
         hairy branched antennae [syn: {water flea}]