Phylum: Charophyta Family: Desmidiaceae
Cosmarium pachydermum P. Lundell
This species would seem to be genuinely scarce. The cell depicted was found in a drainage bog with Sphagnum and other plants
References:
West, W. & West, G.S. (1905) A Monograph of the British Desmidiaceae, Volume 2
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. (2007) Mesotaeniaceae and Desmidiaceae of the European Lowlands
Croasdale, H. & Flint, E.A. (1988) Flora of New Zealand: Desmids, Volume 2