The Collaborative International Dictionary of English v.0.48:

Gregarinae \Greg`a*ri"n[ae]\, prop. n. pl. [NL., fr. Gregarina
   the typical genus, fr. L. gregarius. See Gregarious.]
   (Zool.)
   An order of Protozoa, allied to the Rhizopoda, and parasitic
   in other animals, as in the earthworm, lobster, etc. When
   adult, they have a small, wormlike body inclosing a nucleus,
   but without external organs; in one of the young stages, they
   are am[oe]biform; -- called also Gregarinida, and
   Gregarinaria.
   [1913 Webster]