Phylum: Chlorophyta   Family: Oocysraceae

Oocystis marssonii Lemmermann

One of the large species of Oocystis preferring acidic bogs. Probably widespread in suitable habitat

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