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).