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=5).
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. It differs from C. delicatula by its larger size and the pronounced apertural rim.
Only molecular research can shed light on this problem.