Phylum: Charophyta   Family: Desmidiaceae

Staurastrum arcuatum Nordstedt 1873

A tychoplanktonic species described as common on the continent. It is proving to be scarce in the Outer Hebrides. Coesel & Meesters (2013) describe the semicells as bowl-shaped with relatively long processes. However, the cell-shape is quite variable.

References: 
Nordstedt, C.F.O. (1873) Bidrag till kännedomen om sydligare Norges Desmidiéer.
Coesel, P.F.M. & Meesters, K.J. (2013) European Flora of the Desmid Genera Staurastrum and Staurodesmus.