entozoan

(noun) any of various parasites that live in the internal organs of animals (especially intestinal worms). Synonyms: endoparasite, entoparasite, entozoon, endozoan.

(adj) of or relating to entozoa. Synonyms: endozoan.

(adj) living within a living animal usually as a parasite. Synonyms: entozoic (vs. epizoic), endozoic. Example: "Entozoic worms."