Phylum: Charophyta   Family: Desmidiaceae

Staurodesmus extensus  (O.F. Andersson) Teiling

Common in mildly acidic to neutral waters, in the plankton and marginal vegetation of lochs

References: 
Coesel, P.F.M. & Meesters, K.J. (2013) European Flora of the Desmid Genera Staurastrum and Staurodesmus
John, D.M. & Williamson, D.B. (2009) A Practical Guide to the Desmids of the West of Ireland
Kouwets, F.A.C. (1999) A check-list of desmids (Chlorophyta, Zygnemaphyceae) of France