Phylum: Cynaobacteria   Family: Phormidiaceae

Microcoleus vaginatus Gomont ex Gomont

A common mat-forming species. Found on moist substrates often in mucilage with other algae

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