Phylum: Charophyta   Family: Desmidiaceae

Staurodesmus ralfsii  (West) Tomaszewicz

Found in acidic moorland pools and bogs. Status in the Outer Hebrides uncertain

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