Family: Frontal cirri differ in size and/or pattern from ventral ones of files; "collar" extends short distance along right edge of body; oral area not U-shaped (Illustrated Guide, 1985). Genus: With 2 or more right marginal files of cirri (Illustrated Guide, 1985). Ellipsoid; flexible; posterior rounded; flattened ventral surface with 4-10 rows of cirri; 2 marginal rows; 3 or more frontals; 5-12 anals (Kudo, 1966). Ovoid to elongate with large number of ventral rows of cirri (files); transverse cirri present; frontal cirri undifferentiated from ventrals (Carey, 1992). Species:

50 μm 100 μm 150 μm; x 400

U. trichogaster Stokes: 250-330 μm long; ellipsoid, flexible; about 10 rows of ventrals; many frontals; 2 rows of marginals; 10 anals (How to know the protozoa, 1979).
U. grandis Ehrenberg: 300-400 μm long; macronucleus in 100 or more parts; 6-8 micronuclei (Kudo, 1966).
U. caudata Stokes: About 600 μm long; narrowed anterior part bent to left; peristome 1/3 the body length; macronucleus many (Kudo, 1966).
U. polymicronucleata Merriman: 225 μm long, 65 μm wide; 3 large and 10 small frontals; 4 ventrals; macronucleus in two parts; 3-11 micronuclei (Kudo, 1966).
U. coei Turner: 200 μm long, 50 μm wide; 4 ventrals; 5 frontals; macronucleus in two parts; 4 micronuclei (Kudo, 1966).