Pyxidicula patens – 39 µm
Genus Pyxidicula Ehrenberg, 1938
Diagnosis: shell patelliform or hemispherical, more or less rigid, transparent, speckled; aperture circular, almost the entire diameter of test, or somewhat contracted by an inward margin; a single nucleus; one or more contractile vacuoles.
| 1 | Shell hemispherical | 2 |
| – | Shell flattened, like a disc | 4 |
| 2 | Aperture with a narrow recurved margin | P. operculata |
| – | Aperture with two narrow margins or collars, one curved inwards, the other curved outwards | 3 |
| 3 | Outer collar broader than the inner rim, hyaline, thinner than the rest of the shell and somewhat undulated | P. patens |
| – | Both collars relatively small with the same structure and color as the rest of the shell, not undulated | Pyxidicula spec. |
| 4 | Shell with a flat margin | P. cymbalum |
| – | Shell with a hollow or tube shaped margin | P. invisitata |
