Phylum: Charophyta   Family: Desmidiaceae

Cosmarium subnudum (W. & G.S. West) P.F.M. Coesel & K.J. Meesters 2023

Until recently this was Cosmarium sportella var. subnudum. It has now been raised to species level. West & West (1908: 186, pl. 82: 14) have it as "… abundant among mosses on dripping rocks." This is the situation in the Outer Hebrides where, in such habitats, it can be remarkably abundant. It has also been found in slightly acidic, mesotrophic, loch-margins.
Cell dimensions: L. 47-56 µm; B. 40-49 µm; Is. 11.6-17 µm; Th. 24-27 µm; L/B. 1.05-1.29.

References: 
Coesel, P.F.M. & Meesters, K.J. (2023 second edition). Desmids of the Lowlands.
Kouwets, F.A.C. (in manuscript). European Flora of the Desmid Genus Cosmarium.
Van Westen, M. (2024). Sieralgen in Drenthe.
West, W. & West, G.S. (1908). A Monograph of the British Desmidiaceae, Volume 3.