An order of Protozoa of the class Haplosporea which comprises parasites in skeletal and cardiac muscle of vertebrates. The organisms have a very wide distribution both geographically and in host species, infecting reptiles, birds, and mammals (including marsupials). Humans are occasionally infected by the parasite referred to as Sarcocystis lindemanni. It is doubtful whether Sarcosporida found in different hosts are themselves always different, though this has often been assumed. Host specificity is known not to be strict; however, it is unlikely that there is only one species—S. miescheriana—as proposed by some investigators.