Phylum: Charophyta   Family: Desmidiaceae

Staurodesmus subtriangularis  (O. Borge) E. Teiling 1948

First described and illustrated by Borge (1897: 212, pl. 3: 4) as Arthrodesmus incus var. subtriangularis. Teiling (1948: 64) moved it to the Staurodesmus genus and raised it to species rank.
Cell dimensions: L: 25-31 µm; B: 24-27 µm; Is: 7.5-9.2 µm; Sp: 6-21 µm; Overall LxB: 26-31 x 45-65.
A rare species in Europe, only known from Britain. It would suggest an Atlantic distribution. In the Outer Hebrides it has been found in both shallow and deeper lochs.

References: 
Borge, O. (1897). Algologiska Notiser. 3-4. Zur Kenntnis der Verbreitungsweise der Algen. 3 Süsswasser-Plankton aus der Insel Mull.
Coesel, P.F.M. & Meesters, K.J. (2013). European Flora of the Desmid Genera Staurastrum and Staurodesmus.
Teiling, E. (1948). Staurodesmus, genus novum. Containing monospinous Desmids.