Order: No kinetidal specializations at oral region.
Family (Kahl): Cytostome terminal; ciliation uniform; usually encased in a pseudochitinous lorica (Kudo, 1966).
Genus: Oblong; ciliary circle around cytostome; usually one caudal cilium; with large posterior vesicle containing turbid fluid (Kudo, 1966). Easily recognizable by the transverse annulations of the body and the presence of a large protruding vacuole in posterior (Carey, 1992). Similar to Vasicola, but small and free swimming, without a lorica (How to know the protozoa, 1979).
->> Description at WPRNO Google Image Search
Similar Genus ->> Vasicola
Metacystis sp.1
42 x 13 μm
Japan, 1998
Movies 
Metacystis sp.2
31 x 13 μm
truncata ?
Japan, 1998
Metacystis sp.3
48 x 8 μm
or Vasicola ?
Japan, 1998
