Phylum: Charophyta   Family: Desmidiaceae

Staurodesmus subhexagonus  (W. & G.S. West) P.F.M. Coesel 1993

First described and illustrated by West & West (1912: 96, pl. 114: 6) under the cumbersome name of Arthrodesmus incus var. ralfsii f. subhexagona. Coesel (1993: 110) moved it to the Staurodesmus genus and raised it to species rank.
Cell dimensions: L: 13-16 µm; B: 11-14 µm; Is: 6.1-6.5 µm; Sp: 1.9-5.2 µm; Overall B: 20-28.
A rare species only known in the Outer Hebrides from a deep-water loch.

References: 
Coesel, P.F.M. (1993). Taxonomic notes on Dutch desmids II.
Coesel, P.F.M. & Meesters, K.J. (2013). European Flora of the Desmid Genera Staurastrum and Staurodesmus.
West, W. & West, G.S. (1912). A Monograph of the British Desmidiaceae, Volume 4.