An order of the class Toxoplasmea. Four genera, Toxoplasma, Besnoitia, Sarcocystis, and Encephalitozoon, make up the order. The organisms are parasites of vertebrates. Toxoplasma is often found encysted in nerve tissue, Besnoitia in connective tissue, and Sarcocystis in muscle. Very little is known about Encephalitozoon, but the parasite has been found in the brain of rabbits.