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: 100 μm long; with endosymbiotic algae; fresh water (Kahl, 1930).

31 μm 63 μm 94 μm; x 640

Images of collecting locality: No. 2, Iroha-numa (marsh/bog), Zao mountain, Yamagata city, Yamagata Pref., Japan, August 2, 2006 by Y. Tsukii