Phylum: Charophyta   Family: Desmidiaceae

Cosmarium boeckii J.N.F. Wille 1880

This is similar in size and shape to the rare Cosmarium isthmochondrum but that species has a smoother outline, two prominent subapical granules, a papilla on the basal angles and two pryenoids per semicell. It also shares a supraisthmial granule.
Cell dimensions: L: 31-38 µm; B: 27-34 µm; Is: 8-11 µm; Th: 17.5-21 µm; L/B: 1.07-1.15.
Common in mildly circumneutral waters such as peaty pools, abandoned peat-cuttings, and vegetated loch-margins.

References: 
Kouwets, F.A.C. (2025). European Flora of the Desmid Genus Cosmarium.