Phylum: Cyanobacteria   Family: Nostocaceae

Nostoc sphaericum Vaucher ex Bornet & Flahault

Very similar to Nostoc commune but with slightly smaller cells and heterocysts. Habitat is also similar but tolerates standing water

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