Phylum: Charophyta   Family: Desmidiaceae

Cosmarium granatum var. nordstedtii A. Hansgirg 1888

It differs from the nominate variety by having smaller cells and the lower part of the semicells are straight to slightly divergent and often thickened. It also has a narrower isthmus.
Cell dimensions: L: 28-34 µm; B: 19-24 µm; Is: 6-8 µm; L/B: 1.4-1.55.
Found in mesotrophic, circumneutral waters. Status in the Outer Hebrides unclear due to confusion with similar species.

References: 
Coesel, P.F.M. & Meesters, K.J. (2023 second edition). Desmids of the Lowlands.
Van Westen, M.C. (2024). Sieralgen in Drenthe.