Phylum: Charophyta   Family: Desmidiaceae

Cosmarium pseudotroumousense F.A.C. Kouwets 2025

This newly described species is part of a complex of similar-looking taxa. As the name suggests, it’s rather similar to C. troumousense but on average, slightly larger.
Cell dimensions: L. 26.6-33.3 µm; B. 20.7-28.2 µm; Is. 10-13.8 µm; Th. 14.7-18 µm; L/B. 1.22-1.33.
The status is unknown in the Outer Hebrides. In Europe it has been found with moss-cushions in spring bogs and with moss on dripping rocks. The Outer Hebridean finds have come from semi-permanent rainwater pools in a disused quarry. Found with filamentous algae. Also from ephemeral pools.

References: 
Kouwets, F.A.C. (2025). European Flora of the Desmid Genus Cosmarium. Part 1: Text. Part 2: Plates.