Phylum: Charophyta   Family: Desmidiaceae

Actinotaenium subtile (W. West & G.S. West) E. Teiling 1954

First described by West & West (1897: 479, pl. 6: 8, 9) as Penium subtile. It was later moved to Actinotaenium by Teiling (1954: 410, fig. 61). A small cell, cylindrical with a slight median constriction. Specimens occur with either one or two pyrenoids.
Cell dimensions: 13-22 µm; B: 9-14 µm; L/B: 1.2-1.6.
In their later flora West & West (1904: 92) note: “This is a rare species which occasionally occurs in prodigious quantity in small pools in the best bogs.” This hasn’t been observed in the Outer Hebrides but these small Actinotaenium species are easily misidentified without a good look at the cell-wall structure.

References: 
Coesel, P.F.M. & Meesters, K.J. (2023 second edition) Desmids of the Lowlands.
Ruzicka, J. (1981) Die Desmidiaceen Mitteleuropas, Volume 1, Part 2.
West, W. & West, G.S. (1897) A contribution to the freshwater algae of the south of England.
West, W. & West, G.S. (1904) A Monograph of the British Desmidiaceae, Volume 1.