Phylum: Charophyta   Family: Closteriaceae

Closterium lunula J. Ralfs 1848

First described in Ralfs (1848: 163, pl. 27: 1). West & West (1904: 150, pl. 18: 8-9) specifically mention it being 'general' in the Outer Hebrides.
Cell dimensions: L: 540-700 µm; B: 80-110 µm; Ap: 20-23 µm; L/B: 6-8.
Widespread and can be locally common in acidic peaty pools, bogs, and abandoned peat-cuttings.

References: 
Brook, A.J. & Williamson, D.B. (2010). A Monograph on some British Desmids.
Coesel, P.F.M. & Meesters, K.J. (2023 second edition) Desmids of the Lowlands.
Ralfs, J. (1848). The British Desmidieae.
Van Westen, M. (2024) Sieralgen in Drenthe.