Genus: Body long to ovoid; apex fan-shaped; txicysts evenly distributed along edge of apex (Illustrated Guide, 1985). Body elongate, circular in cross section; antrerior obliquely truncated, surmounted by an unciliated apical ridge, which is lined with trichocysts; cytostome slit-like (Carey, 1992). Very many species (Corliss, 1979). Species: Cell body ovoid, rotund, 255 μm long, with a well-developed anterior (apical ridge thick), macronucleus ellipsoidal (Carey, 1992).

50 μm 100 μm 150 μm; x 400 : 31 μm 63 μm 94 μm; x 640

Images of collecting locality: Yasuragi-no-ike (pond), Oura central park, Oura town, Gunma Pref., Japan, February 2006 by Y. Tsukii

S. syrtis Lepsi, 1964: Cell body ovoid, rotund, 255 μm long, with a well-developed anterior (apiccal ridge thick), macronucleus ellipsoidal (Carey, 1992).

S. extensum Kahl, 1933: cell body long and tubular, 200-250 μm long, anterior truncate and expanded, posterior rounded, trichocyst present in the anterior, macronucleus long and moniliform (Carey, 1992).