Phylum: Charophyta Family: Desmidiaceae
Staurastrum pungens Brébisson 1848
This would seem to be genuinely rare with few records reported. Quite a variable species in relation to its spines. An acidophile found in disused peat-cuttings and similar habitats.
References:
Ralfs, J. (1848) The British Desmidieae.
West, W., West, G.S. & Carter, N. (1923) A Monograph of the British Desmidiaceae, Volume 5.
John, D.M. & Williamson, D.B. (2009) A Practical Guide to the Desmids of the West of Ireland.
Coesel, P.F.M. & Meesters, K.J. (2013) European Flora of the Desmid Genera Staurastrum and Staurodesmus.