coccidium

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

• noun Any of various parasitic apicomplexan protozoans that cause diseases such as toxoplasmosis in the digestive tract of vertebrates.

from The Century Dictionary.

• noun Pl. coccidia (-ä). In botany, a name given by Harvey to a form of conceptacle found in certain red algæ, borne on lateral branches, or sessile on the surface of the frond, and usually not opening by a pore. The spores within are attached to a central placenta.
• noun A genus of gregarines.
• noun [lowercase] One of the coccidiidea.

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

• noun (Microbiol.) any sporozoan of the order Coccidia, parasitic on the digestive epithelium of vertebrates and higher invertebrates. It is the causative agent of coccidiosis, which can be a problem in poultry rearing.

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

• noun parasitic on the digestive epithelium of vertebrates and higher invertebrates