Cosmarium cyclicum. Notice roughly circular cell outline and crenate margins.
Cell dimensions (L x B): 50 x 55 µm
C. cyclicum is a characteristic species, hardly or not to be confused with any other Cosmarium species. Cells are pretty large and almost circular in shape with distinctly crenate margins. Cell wall ornamentation, in the form of radiating series of (bigranulate) verrucae, often is confined to the marginal zone but may extend to the central area as well. In the Netherlands, C. cyclicum is of occasional occurrence in neutral, semi-atmophytic habitats, in particular inundated grasslands.
Largely empty cell of Cosmarium cyclicum showing series of (bigranulate) cell wall verrucae radiating to the periphery.