Phylum: Charophyta   Family: Spirogyracea

Spirogyra jugalis (O.F. Müller) F.T. Kützing 1845

First described and illustrated by Müller (1782: 5, pl. 883) as Conferva jugalis. It was later moved to its current position by Kützing (1845: 223). Most Spirogyra species require conjugation for identification but some of the larger species, such as this one, have their own size-slot.
Cell dimensions: L: 80-400(-600) µm; B: 75-105 µm.
Not common, northern records are from Scotland and Orkney. Found in relatively clear eutrophic water, developing slimy filamentous green masses.

References: 
John, D.M., Whitton, B.A. & Brook, A.J. (2011 second edition). The Freshwater Algal Flora of the British Isles.
Kützing, F.T. (1845). Phycologia germanica, d. i. Deutschlands Algen in bündigen Beschreibungen. Nebst einer Anleitung zum Untersuchen und Bestimmen dieser Gewächse für Anfänger.
Müller, O.F. (1782). Flora danica. Vol. 5.