n. pl.1.(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 amœbiform; - called also Gregarinida, and Gregarinaria.