Phylum: Chlorophyta   Family: Radiococcaceae

Coenococcus planctonicus Korshikov

Colonies usually grouped in tetrads in a mucilaginous envelope. Infrequently recorded but probably overlooked

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