Phylum: Charophyta   Family: Closteriaceae

Closterium juncidum var. robustius A.I. Lobik 1915

First described by Lobik (1915: 325) without illustration. He notes: “The thickness of the ends is quite constant in all cases, namely, 5-5.5 µm. The shell is colored, striated, 5 striations are visible at a time; each half-cell has 6 pyrenoids.” Cells from the Outer Hebrides show 4-5 striae (costae) in face view. There is a distinct apical pore visible not mentioned by other authors. Quite a distinct taxon that might well justify being described as a full species.
Cell dimensions: L: 210-275 µm; B: 8.8-9.6 µm; Ap: 4.4-4.9 µm; L/B: 22-31.
Rarely encountered in acidic oligotrophic moorland pools and peaty bogs. Possibly an Arctic-Atlantic species. Lobik’s original finds came from the eastern end of the Gulf of Finland.

References: 
Brook, A.J. & Williamson, D.B. (2010). A Monograph on some British Desmids.
Lobik, A.I. (1915). Note sur les desmidiacées récoltées par M. Perfiliev aux environs de Sestroretsk (gouv. Petrograd).