||Greg`a*ri"næ (?), n. pl. [NL., fr. Gregarina the typical genus, fr. L. gregarius. See Gregarious.] (Zoöl.) 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 amœbiform; -- called also Gregarinida, and Gregarinaria.