Genus: Test circular, ovoid or discoid; pseudostome eccentric, circular or ovoidal; with or without spines (Kudo, 1966). Species: Pseudostome more or less central; test variable in shape and size; diameter 187-325 μm; with 0-12 spines; opaque or semitransparent; with fine sand-grains or diatom shells (Cojima, Sudo, Chihara eds., 1995).

Similar species -->> C. ecornis (lack spines)

50 μm 100 μm 150 μm; x 400