Phylum: Charophyta   Family: Desmidiaceae

Staurodesmus dejectus   (Brébisson) Teiling

Not uncommon in moorland pools, peat hollows and the plankton 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