Cosmarium tetrachondrum. Cell with vital chloroplast holding a single, central pyrenoid.

Cell dimensions (L x B): 23 x 26 µm



Desmid of the month
July 2016

Cosmarium tetrachondrum

Cosmarium tetrachondrum, although small-sized and but little remarkable in shape, may be readily identified by its four distinct granules at the base of each semicell. Semicells are depressed semicircular in outline with smooth to weakly undulate lateral margins. The basal granules characteristic of the species are placed on either side of the isthmus. Next to this relatively large isthmial granules often some addtional, but much smaller intramarginal granules may be observed near the basal angles. In Europe, C. tetrachondrum is a rare species with a distinct atlantic distribution. In the Netherlands, at present, it is only known from a single mesotrophic fen area in the province of Friesland.

Empty cell of C. tetrachondrum showing the pronounced, big granules near the isthmus characteristic of this species. Notice also some small granules at the margins of the lower semicell and widely distributed, vague pore fields all over the cell wall.



Empty semicell of C. tetrachondrum in isthmial view showing the tetrad of big granules around the isthmus.