Phylum: Charophyta   Family: Desmidiacea

Cosmarium triomphalum (R. Gutwinski) W. Schmidle 1898

Semicells depressed trapeziform, sinus linear and closed. In face-view there are about 5 crenae along each side, which become emarginate towards the apex. Apex truncate with 4-crenae. The main distinguishing character of the cell-wall is the two supraisthmial granules. It also has a series of intramarginal granules.
Cell dimensions: L: 24-28 µm; B: 20-23.4 µm; Is: 6.9-8.6 µm; C.12-15 µm; L/B: 1.13-1.21.
A reasonably common species found in the tychoplankton of circumneutral waters.

References: 
Kouwets, F.A.C. (2025). European Flora of the Desmid Genus Cosmarium. Part 1: Text. Part 2: Plates.
Van Westen, M. (2024). Sieralgen in Drenthe.