Phylum: Charophyta   Family: Desmidiaceae

Staurastrum simonyi var. sparsiaculeatum  (W. Schmidle) M. Hirano 1953

It differs from the nominate variety in have additional lateral spines quite randomly displayed. Also, the apical view differs in having truncate angles instead of pointed.
Single cell dimensions: L: 23.4 µm; B: 24.1 µm; Is: 6.1 µm.
Found in mildly acidic mesotrophic waters. There is room for confusion as this variety is not always easy to tell from the nominate in face view.

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