Phylum: Charophyta   Family: Desmidiaceae

Micrasterias pinnatifida  J. Ralfs 1848

First described and illustrated by Ralfs (1848: 77, pl. 10: 3). West & West (1905: 82) note: “This is one of the most abundant species of the genus, more especially in Sphagnum-bogs and pools in upland districts."
Cell dimensions: L: 50-80 µm; B: 50-85 µm; Is: 12-18 µm; L/B: 0.8-1.0.
Maybe not as common as in the Wests days but fairly frequently found.

References: 
Coesel, P.F.M. & Meesters, K.J. (2023 second edition) Desmids of the Lowlands.
Ralfs, J. (1848) The British Desmidieae. Ruzicka, J. (1981) Die Desmidiaceen Mitteleuropas, Volume 1, Part 2.
West, W. & West, G.S. (1905) A Monograph of the British Desmidiaceae, Volume 2.