Phylum: Charophyta   Family: Desmidiaceae

Staurodesmus mucronatus (C. Nägeli) K. Thomasson 1955

A small cell with a wedge-shapes sinus. Semicells are elliptical with very small, laterally inserted, spines.
Single cell dimensions: L: 21.3 µm; B: 21.8 µm; Is: 5.9 µm; Sp: 1-0 µm; Overall B: 24.
West, West & Carter (1923: 12), as Staurastum mucronatus, record its distribution in Scotland as general but scarce. It is proving to be quite rare in the Outer Hebrides. Found in acidic waters.

References: 
Coesel, P.F.M. & Meesters, K.J. (2013). European Flora of the Desmid Genera Staurastrum and Staurodesmus.
Teiling, E. (1967). The Desmid Genus Staurodesmus. A taxonomic study.
West, W., West, G.S. & Carter, N. (1923). A Monograph of the British Desmidiaceae, Volume 5.