Phylum: Charophyta   Family: Desmidiaceae

Cosmarium corbula L.A. de Brébisson 1856

A variable species with some similarity to C. sportella and was a variety of that species originally. The latter species has a slightly different granular pattern and is a bit larger.
Cell dimensions: L: 29-34 µm; B: 28-32 µm; Is: 10-11.5 µm; Th: 16.6-21 µm; L/B: 1.04-1.07.
A rare species in the Outer Hebrides. Found in slightly acidic to mildly alkaline waters such as loch-margins with little vegetation.

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