Phylum: Charophyta   Family: Desmidiaceae

Staurodesmus corniculatus var. spinigerus (W. West) H.T. Croasdale 1957

A small cell with a wide-open sinus from a notched extremity. Subtriangular semicells with slightly concave side, the upward-pointing apical angles support a small spine. Cells are predominantly triradiate, but quadri-radiate cell have been recorded. According to West & West (1912: 164) it differs from the nominate variety in being smaller and supporting short spines.
Single cell dimensions: L: 25 µm; B: 22.2 µm; Is: 9.2 µm; Sp: 1.5 µm; overall L: 28.
A rare species found in slightly acidic waters, usually in the plankton of mesotrophic shallow lochs. It would appear to have an Atlantic distribution.

References: 
West, W. & West, G.S. (1912). A Monograph of the British Desmidiaceae, Volume 4.