Phylum: Charophyta   Family: Desmidiacea

Cosmarium tetraophthalmoides F.A.C. Kouwets 2025

Similar in size and habitat requirements to Cosmarium tetraophthalmum but having smaller and more numerous granules. In face-view up to 16 granules can been seen on each side of the semicell. Parts of the cell-wall can be totally lacking in granules and is finely punctate.
Kouwets’ cell dimensions: L: 90-104 µm; B: 61-71 µm; Is: 19-22 µm; Th: c.47; L/B: 1.46-1.51.
Mine – single cell: L: 101 µm; B: 69 µm; Is: 23 µm; L/B: 1.49.
Because of the confusion with C. tetraophthalmum, its status in the Outer Hebrides in unclear.

References: 
Kouwets, F.A.C. (2025). European Flora of the Desmid Genus Cosmarium.