endoparasite

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A parasite, such as a tapeworm, that lives within another organism.

from The Century Dictionary.

• noun An internal parasite; a parasite which lives in the internal parts or organs of the host, as distinguished from an ectoparasite, which infests the skin or surface. The entozoans are of this character. The term has no classificatory meaning.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Zoöl.) Any parasite which lives in the internal organs of an animal, as the tapeworms, Trichina, etc.; -- opposed to ectoparasite. See entozoön.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A parasite that lives inside the body of an organism, such as a tapeworm.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun any of various parasites that live in the internal organs of animals (especially intestinal worms)