Phylum: Charophyta   Family: Desmidiaceae

Staurastrum manfeldtii var. annulatum W. & G.S. West 1902

The original diagnosis (West & West 1902: 56): “The double ring of granules round the base of the semicells and the slight reduction of the apical emarginate warts are characters which at once distinguish this variety.” The significant character of this variety is the double ring of basal granules. However, the armature on the specimen below is more robust than is typical.
Overall cell dimensions (2): L: 52.9-55.5 µm; B: 77-89 µm; Is: 11.2-12.3 µm; L/B: 0.6-72.
Found in the vegetated margins of lochs that are slightly alkaline to slightly acidic. It would appear to be a rare taxon in the Outer Hebrides.

References: 
Coesel, P.F.M. & Meesters, K.J. (2013). European Flora of the Desmid Genera Staurastrum and Staurodesmus.
West, W. & West, G.S. (1902). A contribution to the freshwater algae of the North of Ireland.