Phylum: Charophyta   Family: Desmidiaceae

Staurodesmus controversus (W. & G.S. West) E. Teiling 1967

A small cell with wide-open sinuses from an angular or rounded base. Semicells sub-cuneate with a convex, or occasionally, truncate apex. Tiny parallel spines occur at the apical-lateral angles. Cells are biradiate.
Cell dimensions (2): L: 14-14.8 µm; B: 14-15.2 µm.; Is: 7.7-8 µm; Sp: 1.0-3.0; overall B: 16-19.
A rare species, most likely to be found in Atlantic regions 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.