Phylum: Charophyta   Family: Desmidiaceae

Staurastrum brevispina L.A. de Brébisson 1848

First described by Brébisson in Ralfs (1848: 124, pl. 34: 7) and illustrated by Jenner. A variable species that has produces some varieties. This nominate variety is as broad as longer to slightly longer than broad. The apices are usually convex.
Cell dimensions: L: 34-40 µm; B: 30-40 µm; Is: 11-14 µm; L/B: 1.06-1.17.
Prefers slightly acidic habitats and found in the plankton of shallow, vegetated lochs. Widespread in the Outer Hebrides but not that common.

References: 
Coesel, P.F.M. & Meesters, K.J. (2013) European Flora of the Desmid Genera Staurastrum and Staurodesmus.
Ralfs, J. (1848) The British Desmidieae.
West, W., West, G.S. & Carter, N. (1923) A Monograph of the British Desmidiaceae, Volume 5.