Phylum: Charophyta   Family: Desmidiaceae

Staurastrum chavesii var. latiusculum (West & G.S. West) Coesel & Meesters 2013

Both the nominate and this variety are very rare, the latter only known from Ireland. The habitat is acidic oligotrophic moorland bogs and pools, also associated with Sphagnum. This differs from the nominate variety in having 3 (4?) short spines at the ends of the processes and spines at the base of the processes (but not always easy to see).

References: 
West, W., West, G.S. & Carter, N. (1923) A Monograph of the British Desmidiaceae, Volume 5.
Coesel, P.F.M. & Meesters, K.J. (2013) European Flora of the Desmid Genera Staurastrum and Staurodesmus.