dinoflagellate

from WordNet (r) 3.0 (2006)

dinoflagellate
    n 1: chiefly marine protozoa having two flagella; a chief
         constituent of plankton

from The Collaborative International Dictionary of English v.0.48

dinoflagellate \dinoflagellate\ n.
   a member of the {Dinoflagellata}, chiefly marine protozoa
   having two flagella. The dinoflagellates form a chief
   constituent of plankton.
   [WordNet 1.5]