Phylum: Charophyta   Family: Desmidiaceae

Cosmarium corbula (L.A. de Brébisson) 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: 29.6-30.3 µm; B: 28.1-29.2 µm; Is: 10.1-10.3 µm; Th: 16.6 µm; L/B: 1.04-1.06.
A rare species with just one record from the Outer Hebrides. Found in a slightly acidic loch with very little vegetation.

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