Image © Henk Schulp
Cosmarium quinarium. Notice trapeziform semicells with broadly rounded angles and slightly convex sides being marked with distant granules. Chloroplasts with two big pyrenoids each.
Cell dimensions (L x B): 40 x 32 µm
Cosmarium quinarium belongs to a group of granulate Cosmaria in which the granules are not uniformly distributed over the cell wall. The species in question is characterized by semicells that, in frontal view, are trapeziform in outline with broadly rounded angles and slightly convex sides. Cell wall ornamentation is in the form of a marginal and an intramarginal series of marked, rather distant granules. In addition to that, in the nominate forma there are 5 big granules in the semicell centre disposed in two transverse series. In forma irregularis, on the contrary, those granules number up to nine not being arranged in any specific pattern. In the Netherlands C. quinarium is a rare species characteristic of acidic, slightly minerotrophic bog pools.
Dead, for the greater part empty cell of C. quinarium. Notice pattern of cell wall sculpturing in the semicell centre, i.e. an upper transversal series of 3 and a lower transversal series of 2 big granules.
Image © Koos Meesters.
Another empty cell (in early stage of division) of C. quinarium forma irregularis.