Phylum: Charophyta   Family: Desmidiaceae

Staurastrum subnivale  E. Messikommer 1942

The semicells are cup-shaped and have simple spines around the decumbent processes but barely noticeably on the apex. There is a ring of granules at the base of the semicells. The processes are tipped with 4 short spines. Compare with St. borgeanum, which is stockier with shorter processes, and St. inflexum, which is smaller with little or no overlap in cell dimensions. The semicells of both species are twisted at the isthmus.
Single cell dimensions: L: 28.8 µm; B: 37 µm; Is: 6.7 µm; L/B: 0.78.
A seemingly rare species in the Outer Hebrides but may have been overlooked or misidentified in the past.

References: 
Coesel, P.F.M. & Meesters, K.J. (2013). European Flora of the Desmid Genera Staurastrum and Staurodesmus.
Van Westen, M.C. (2024). Sieralgen in Drenthe.