Family: Cirral files spiral obliquely around body.
Genus: Slender or ovoid or fusiform; usually 4 spiral rows of crri; sometimes tube-dwelling (Kudo, 1966). Body long with pointed anterior; loricate; posterior of body blunt, round (Illustrated Guide, 1985). S. gracilis posterior end pointed (Carey, 1992).
Species: 130-200 μm long; fresh water (Kudo, 1966).

S. aculeata Wrzesnioski, 1884: Spindle-shaped; posterior end rounded; thin neck; 90 μm long; peristome 1/2 the body length; contractile vacuole anteriorly located; two ovoid macronuclei (Carey, 1992).

S. secunda Perty: 130-200 μm long; fresh water (Kudo, 1966).