Phylum: Charophyta   Family: Desmidiaceae

Xanthidium impar (J.P. Jacobsen) G. Deflandre 1929

A medium-sized cell with oblong-trapeziform semicells. Sinuses open with a rounded extremity, basal margins slightly convex leading to a mamillate angle bearing a long spine. Apical angles are also mamillate with another long spine. The lateral and apical margins between the spines quite deeply concave. Occasionally, secondary spines can be observed but these are random.
Cell dimensions: L: 35-38 µm; B: 30-34 µm; Is: 10-12 µm; Sp: 9-14 µm; Overall LxB: 56-61 x 52-57 µm.
A very rare desmid found in acidic moorland pools and bogs. In would appear to have a North Atlantic and Alpine distribution.

References: 
John, D.M. & Williamson, D.B. (2009). A Practical Guide to the Desmids of the West of Ireland.
Tsarenko, P.M., Wasser, S.P. & Nevo, E., editors, (2014). Algae of Ukraine, Volume 4: Charophyta.