Diagnosis: Test rounded in dorsal view, usually slightly broader than long, yellowish to brown; some tests are relatively smooth, others are densely covered with amorphous mineral particles; the test is slightly higher than half the test diameter and hardly compressed in the anterior region, above the aperture. Never bearing spines; ventral surface flattened. Aperture invaginated, ovoid, elliptical or circular, eccentric, its anterior edge connected to the inner and anterior-dorsal wall of the shell by a small dark flange with two struts. Its most peculiar feature is the structure of the pseudostome: it is surrounded by a rim or thick ring, usually slightly darker than the rest of the test.
Dimensions: Length 51-74 µm (mean 63.1 µm); width 53-76 µm (mean 64.6 µm); pseudostome 15-20 X 11-20 µm (mean 15.5 X 13.6 µm) n=12. Height: 29-41 µm (n=3).
Ecology: Freshwater. In caves in Croatia.
Remarks: The closest morphological relatives are C. laevigata that is much larger (120-150 µm), C. malvinensis, that has the same size and apertural border but two lateral flanges in the middle part, and C. obscurus that differs by the absence of a clear rim around the aperture and the absence of any struts. Only molecular research can shed light on this problem.