Phylum: Charophyta   Family: Desmidiaceae

Cosmarium groenlandicum (F.C.E. Børgesen) F.A.C. Kouwets 2025

West & West (1908: 120) record for Cosmarium capitulum var. groenlandicum Børgesen 1894: “We have only observed this variety in the Scottish and Irish plankton, in which it is sometimes not uncommon.” Kouwets (2025: 250) notes dimensions as “somewhat longer than broad”, but his drawings measure much closer to L/B: 1.00, which is more in line with the few Outer Hebridean finds.
Cell dimensions: L: 18-22 µm; B: 18-22 µm; Is: 6.7-7.7 µm; Th: c.11 µm; L/B: 0.93-1.04.
A rare desmid found with loch-side vegetation in mildly acidic waters.

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