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]WordNet (r) 3.0 (2006):
dinoflagellate n 1: chiefly marine protozoa having two flagella; a chief constituent of plankton