Phylum: Charophyta   Family: Mesotaeniaceae

Mesotaenium kramstae E. Lemmermann 1896

Cells cylindrical with broadly rounded poles, often slightly curved.
Coesel and Meesters’ cell dimensions: L: 42-104 µm; B: 9-13 µm; L/B: 9-13.
It occurs in meso-oligotrophic, weakly acidic waters, often with mosses. It would appear to be rather scarce in the Outer Hebrides, or elusive.

References: 
Coesel, P.F.M. & Meesters, K.J. (2023 second edition). Desmids of the Lowlands.