Phylum: Charophyta   Family: Desmidiaceae

Staurodesmus cuspidatus  (Brébisson ex Ralfs) Teiling

Common in fairly acidic to mildly alkaline waters such as the plankton of lochs and moorland bogs and pools

References: 
John, D.M. & Williamson, D.B. (2009) A Practical Guide to the Desmids of the West of Ireland
Coesel, P.F.M. & Meesters, K.J. (2013) European Flora of the Desmid Genera Staurastrum and Staurodesmus