Phylum: Charophyta   Family: Desmidiaceae

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

Cells with an extended isthmus and decurrent spines are typical. Cells with parallel spines are included here mainly after West & West (1912: 96, pl. 114: 6) under the cumbersome name of Arthrodesmus incus var. ralfsii f. subhexagona.
Cell dimensions: L: 13-23 µm; B: 11-25 µm; Is: 6-11 µm; Sp: 1.9-5.2 µm; Overall B: 20-34.
A rare species only known in the Outer Hebrides from a deep-water loch and shallow loch-margins.

References: 
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.