Phylum: Cyanobacteria   Family: Coelosphaeriaceae

Coelosphaerium kuetzingianum Nägeli

Colonies are free-floating and found in the plankton of mesotrophic waters. Possibly common but status for the Outer Hebrides uncertain

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