Phylum: Charophyta   Family: Desmidiacea

Staurastrum pingue Teiling

Thought to be fairly common in slightly alkaline waters, especially with plankton. Easily confused with similar species

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