Phylum: Charophyta   Family: Desmidiaceae

Staurastrum lunatum J. Ralfs 1848

First described by Ralfs (1848: 124, pl. 34: 12) and illustrated by Jenner. Similar in shape to S. avicula but with a single spine at the upper angles, sometimes little more than a spicule.
Cell dimensions: L: 30-35 µm; B: 33-40 µm; Is: 9-12 µm.
A common acidophile, found in moorland bogs and abandoned peat-cuttings.

References: 
Ralfs, J. (1848) The British Desmidieae.
West, W., West, G.S. & Carter, N. (1923) A Monograph of the British Desmidiaceae, Volume 5.