Phylum: Charophyta   Family: Desmidiaceae

Cosmarium parviregnellii F.A.C. Kouwets 2025

One of several small, smooth-walled desmids. The main characteristics are lower sides straight to marginally divergent, upper sides convergent and retuse to varying degrees, apex truncate usually with a median dent.
Cell dimensions: L: 12.3-14.4 µm; B: 10.8-13.4 µm; Is: 4.2-4.6 µm; Th: 6-7 µm; L/B: 1.08-1.20.
Status in the Outer Hebrides is uncertain due to earlier taxonomic confusion. It would seem to prefer circumneutral waters such as loch-margins, moorland pools and semi-permanent rainwater pools.

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