Phylum: Charophyta   Family: Desmidiaceae

Staurodesmus cuspidatus (L.A. de Brébisson ex J. Ralfs) E. Teiling 1967

First described by Brébisson in Ralfs (1848: 122, pl. 21: 1a-e; pl. 33: 10) as Staurastrum cuspidatum and illustrated by Jenner. It was later moved by Teiling (1967: 534) to its current genus. An extremely variable species both in terms of the extension of the isthmus and the length of the spines.
Cell dimensions: L: 24-39 µm; B: 20-44 µm.; Is: 5-11 µm; Sp: 4-21.
Zygospore: minus projections: 26-28 µm; overall: 42-44 µm.
Very common in fairly acidic to mildly alkaline waters such as the plankton of lochs and moorland bogs and pools.

References: 
Coesel, P.F.M. & Meesters, K.J. (2013). European Flora of the Desmid Genera Staurastrum and Staurodesmus.
Ralfs, J. (1848). The British Desmidieae.
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.