Phylum: Charophyta   Family: Closteriaceae

Closterium closterioides var. intermedium (J. Roy & Bisset) Ruzicka

The only different between this variety and the nominate is the size, being less than half. An acidophile that tolerated very slightly alkaline conditions. Found in peaty pools and loch-margins with vegetation. It's much rarer than the nominate

References: 
Brook, A.J. & Williamson, D.B. (2010) A Monograph on some British Desmids
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