Phylum: Charophyta   Family: Desmidiaceae

Staurastrum borgeanum  W. Schmidle 1898

The sinus is V-shaped and opens widely. Semicells are cup-shaped or subcuneate, which differs from the similar St. proboscideum (Brébisson) Archer 1861, which are broadly fusiform. The latter species prefers a slightly less acidic ecology.
Cell dimensions: L: 32-35.4 µm; B: 30-37 µm; Is: 10.7-11.4 µm; L/B: 1.01-1.18.
A common species found in acidic, oligo-mesotrophic, waters such as moorland pools and bogs including with Sphagnum.

References: 
Coesel, P.F.M. & Meesters, K.J. (2013). European Flora of the Desmid Genera Staurastrum and Staurodesmus.