Phylum: Chatophyta Family: Desmidiaceae
Staurastrum oxyacanthum var. polyacanthum Nordstedt
Larger than the nominate including a broader isthmus. Both the nominate and this variety would appear quite rare. Found with vegetation in circumneutral waters
References:
West, W., West, G.S. & Carter, N. (1923) A Monograph of the British Desmidiaceae, Volume 5
Coesel, P.F.M. & Meesters, K.J. (2013) European Flora of the Desmid Genera Staurastrum and Staurodesmus
Tsarenko, P.M., Wasser, S.P. & Nevo, E. editors (2014) Algae of Ukraine, Volume 4: Charophyta
Kouwets, F.A.C. (1999) A check-list of desmids (Chlorophyta, Zygnemaphyceae) of France