The Telosporasida and the Coccidia Proper
All members of the class Telosporasida are parasitic. They have simple spores, without polar filaments. (The spore has been lost secondarily in a few genera. ) Each spore contains 1 to many sporozoites. Pseudopods, cilia and flagella are absent, except for flagellated microgametes in some groups. Locomotion is by body flexion or gliding. Reproduction is both sexual and asexual, and there may or may not be alternation of generations. Most Telosporasida are saprozoic, but a few, including the trophozoites of the malaria parasite, are holozoic.
Most of the Telosporasida probably arose from the Mastigasida, but some may have arisen from the Sarcodasida. However, it is difficult to be sure of their origin because of their lack of the usual organelles of locomotion.
The classification of this and related groups is still the subject of considerable difference of opinion among taxonomists, and that used in this book is not considered definitive. It may require several generations of parasitologists to work out a universally acceptable one. This class is divided into 2 subclasses, of which the Gregarinasina parasitize invertebrates and the Coccidiasina occur in both vertebrates and invertebrates. In the latter group, the mature trophozoite is ordinarily intracellular and comparatively small.
The coccidia and their relatives belong to the order Eucoccidiorida. In this order, schizogony is present and the life cycle involves both sexual and asexual phases. Members of the order are found in the epithelial and blood cells of vertebrates and invertebrates.
The coccidia proper belong to the suborder Eimeriorina, which is differentiated from the other 2 suborders by several features of its life cycle. The macrogamete and microgametocyte develop independently, the microgametocyte produces many microgametes, the zygote is not motile, and the sporozoites are typically enclosed in a sporocyst. All the coccidia of domestic animals and man, with one possible exception, belong to two families, the Eimeriidae and Cryptosporidiidae. Another family, the Lankesterellidae, is of considerable interest. Becker (1934) wrote a classic review of the coccidia. Orlov (1956) discussed those of domestic animals, but was seriously handicapped by lack of information about non-Russian work. Becker (1956) and Pellerdy (1956, 1957) have given checklists of the species of coccidia. The coccidia of the avian orders Galliformes, Anseriformes and Charadriiformes were reviewed by Levine (1953).