daph·nia /ˈdæfniə/
  水蚤
  Daph·ni·a n.  Zool. A genus of the genus Daphnia.
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  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]