Phylum: Charophyta   Family: Desmidiaceae

Staurastrum hexacerum V.B. Wittrock 1872

A small desmid with the semicells about fusiform with truncate processes tipped with tiny spines. Semicells often twisted at the isthmus. In apical view predominantly triradiate with slightly concave sides.
Single cell dimensions: L: 28 µm; B: 30 µm; Is: 11.1 µm; L/B: 0.94.
Found in slightly acidic waters often with plankton and weedy margins. Described as widespread in Europe but proving to be scarce in the Outer Hebrides. However, confusion with similar species in the past is possible.

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