Phylum: Chlorophyta   Family: Microsporaceae

Microspora wittrockii (Wille) Lagerh.

Reportedly widespread but infrequent. Similar to Microspora amoena but not showing the 'H' sections

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