Members of this family have a single flagellum. They lack chromatophores or a stigma.
The body is elongate ovoid, with an elongate reservoir at the anterior end into which a contractile vacuole discharges. The single flagellum arises from a blepharoplast at the base of the reservoir. The nucleus is vesicular, with a large endosome. Permanent fusion followed by encystment takes place. Nutrition is holozoic on bacteria.
Copromonas subtilis Dobell, 1908 (syn., Copromonas ruminantium) was first described from the feces of frogs and toads, but has since been found in the feces of man and various domestic and wild mammals. Wenyon (1926) and Noble (1956) found it in pig feces. Woodcock (1916) found it in goat feces. Noble (1958) found that it appeared in fecal samples from Wyoming elk, bison, cattle, horses, sheep and moose after storage at 4° C for 7 to 11 days. It persisted from 2.5 months in the bison samples to more than 18 to 24 months in the elk and cattle samples. It failed to survive in soil or in soil mixed with boiled feces, nor could it be found in soil samples taken from areas where elk, sheep or horses were present.
The trophozoites of C. subtilis are 7 to 20 u long. They are usually ovoid, but can change from spindle-shaped to almost round. The flagellum is 1 to 2 times the length of the body. When the animal swims straight, only the tip of the flagellum moves; the flagellum is sometimes used like a highly flexible probe. The cysts are ovoid or spherical and 7 to 8 u long. They have a thin wall and clear contents with a single vesicular nucleus.
Reichenow (1952) and Grasse (1952) considered that Copromonas subtilis is a synonym of Scytomonas pusilla Stein, 1878, which was incompletely described by Stein.
In this order a single large green chromatophore is typical. The stored reserves are starch and sometimes lipids. No members of this order are parasites of domestic animals or man, but one species deserves mention.
Polytoma uvella Ehrenberg, 1838 occurs in infusions and stagnant water, and has been found in bull sheath washings submitted for Tritrichomonas foetus diagnosis (Morgan and Hawkins, 1952). Its body is ovoid to piriform, 15 to 30 by 9 to 20 u, without chromatophores and with numerous starch granules in the posterior part of the body. A red or pink stigma may or may not be present. There are 2 anterior flagella of equal length.