Phylum: Chlorophyta   Family: Radiococcaceae

Radiococcus planktonicus J.W.G. Lund

Thought to be widespread in lakes and lochs but easily confused with other planktonic algae

References: 
John, D.M., Whitton, B.A. & Brook, A.J. (2011) The Freshwater Algal Flora of the British Isles