Phylum: Chlorophyta   Family: Oedogoniaceae

Oedogonium undulatum A. Braun ex K.E. Hirn 1900

First described and illustrated by Braun in Hirn (1900: 257, pl. 45: 272-275). This one of the easiest filamentous algae to identify with the undulate cell-walls.
Cell dimensions: L: 50-71 µm; B: 15-22 µm.
Oospore diameters: 42-52 µm.
A widespread species but not common. Found in phytoplankton and marginal vegetation in moorland pools and shallow bogs.

References: 
Hirn, K.E. (1900) Monographie und iconographie der Oedogoniaceen.
John, D.M., Whitton, B.A. & Brook, A.J. (2011 second edition) The Freshwater Algal Flora of the British Isles.