Phylum: Charophyta   Family: Closteriaceae

Closterium directum  W. Archer 1862

A variable species in several respects: it can be straight to cambered; the cell-wall can have medium noticeable striae, faint striae or seemingly lacking, even under high magnification; the apices can be truncate of reflexed. The terminal vacuole has a single crystal that can be compound. It can also present a considerable size range, partly due to dividing cells.
Cell dimensions: L: 188-410 µm; B: 12.8-17 µm; Ap: 7-11 µm; L/B: 14-32.
A common acidophile of moorland pools and bogs.

References: 
Brook, A.J. & Williamson, D.B. (2010). A Monograph on some British Desmids.
Coesel, P.F.M. & Meesters, K.J. (2023 second edition). Desmids of the Lowlands.