d8Gregarin91\"d8Greg`a*ri"n\"91\, n. pl. [NL., fr. Gregarina the typical genus, fr. L. gregarius. See Gregarious.] (Zo["o]l.) 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.