Phylum: Charophyta   Family: Desmidiaceae

Cosmarium volcanicum F.A.C. Kouwets 2025

This recently described species was found in the French Auvergne in oligo-mesotrophic lakes. It is very similar to C. cantalense, found in similar habitats. The latter species is slightly broader giving a small L/B ratio.
Single cell dimensions: L: 15.9 µm, B: 14.8 µm, Is: 5.6 µm; Th: 8.9 µm, L/B: 1.08.
Found in slightly acidic, mesotrophic habitats. Because of the uncertainty over identification its status in the Outer Hebrides is unknown. Now we have a clearer picture of these small smooth-walled species, thanks to Kouwets (2025), their general distribution should become more apparent.

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