<zoology> 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 amoebiform. ... Synonym: Gregarinida, and Gregarinaria. ... Origin: NL, fr. Gregarina th...