Members of this family have a single flagellum.
Members of this genus lack chromatophores, lorica or test. They are solitary. The nucleus is near the center of the body. The single flagellum arises from a basal granule near the body surface. Cysts are formed, at least in the free-living species. This genus is the colorless homolog of Chromulina. Its parasitic species are poorly known.
Oikomonas communis Liebetanz, 1910 and Oikomonas minima Liebetanz, 1910 were both described from the rumen of cattle. They are said to differ in size, the former being up to 11 u long and the latter more than 4 u long; this is probably not a valid difference. Das Gupta (1935) found O. communis in the rumen of goats in India.
Oikomonas equi Hsiung, 1930 was found in the cecum of 8 horses in Iowa. It is usually spherical or ovoid and swims in a jerky manner. The nucleus has a large, central endosome and the cytoplasm is filled with small, dark-staining granules. The body is 3.5 to 7 u long and 3 to 5.5 u wide. The flagellum is about 20 u long.
The body is spherical or ellipsoidal, with a more or less central nucleus. A single, long flagellum arises from a basal granule on the nuclear membrane. This genus is poorly known and has apparently not been studied by modern methods. It is closely related to Oikomonas and may even be a synonym of that genus. Several species have been named, all parasitic, but most of them are probably the same.
Sphaeromonas communis Liebetanz, 1910 (syns., S. minima, S. maxima, S. liebetanzi, S. rossica) occurs in the rumen of the ox and goat and in the cecum and feces of the guinea pig. It may also be coprophilic. Liebetanz (1910) and Braune (1914) found it in the rumen of cattle in Europe, Becker and Talbott (1927) found it in the rumen of a few cattle in Iowa (calling it, however, Monas communis), and Fonseca (1916) found it in cattle and goats and also in the guinea pig in Brazil. Yakimoff et al. (1921) found it in the guinea pig in Russia. The body is spherical or ellipsoidal, 3 to 14 u in diameter. The cytoplasm contains many dark-staining granules.
The body is naked, without chromatophores and with a vesicular nucleus at the anterior end. One flagellum arises from the nuclear membrane. A band-like peristyle arises from the nuclear membrane opposite to the origin of the flagellum and extends posteriorly along the periphery of the body surface; it stains with hematoxylin and protargol. Cytostome and contractile vacuoles are absent.
Caviomonas mobilis Nie, 1950 occurs in the cecum of the guinea pig. The body is ovoid to elongate carrot-shaped and the posterior end is often pointed. It measures 2 to 7 by 2 to 3 u with a mean of 4 by 3 u.