Phylum: Charophyta   Family: Desmidiaceae

Pleurotaenium nodulosum (J. Ralfs) A. de Bary 1858

Quite variable in shape: some semicells are parallel for most of their length while others taper to the apices from about halfway. Shallow undulations are usually confined to the basal part. The apical whorl of granules also varies in size.
Cell dimensions: L: 400-600 µm; B: 40-70 µm; L/B: 7-12.
West & West (1904: 200), as a variety of Pl. coronatum, describe it as widely distributed and most abundant. This is still the status for the Outer Hebrides. Found in mildly acidic habitats such as moorland pools and bogs, also in shallow loch-margins.

References: 
Coesel, P.F.M. & Meesters, K.J. (2023 second edition). Desmids of the Lowlands.
Van Westen, M.C. (2024). Sieralgen in Drenthe.
West, W. & West, G.S. (1904). A Monograph of the British Desmidiaceae, Volume 1.