Phylum: Charophyta   Family: Zygnemataceae

Mougeotia ovalis (A.H. Hassall) V.B. Wittrock & C.F.O. Nordstedt 1886

First described by Hassall (1843: 187, pl. 7: 15) as Sphaerocarpus ovalis but that genus does not appear to have been designated. It was moved to Mougeotia by Wittrock & Nordstedt (1886: 136). John et al. (2011: 585) record it as rare in the British Isles. As the specific epithet suggests, the zygospores are oval in shape with fine scrobiculation of the wall (difficult to see with the light microscope).
Cell dimensions: L: 110-140 µm, B: 11-14 µm.
Zygospore: L: 29-41 x B: 24-39 µm.
Rare, found in the same habitat as Mougeotia viridis: in moorland bogs and pools with variable acidity.

References: 
Hassall, A.H. . (1843) Descriptions of British freshwater Confervae, mostly new, with observations on some of the genera.
John, D.M., Whitton, B.A. & Brook, A.J. (2011 second edition) The Freshwater Algal Flora of the British Isles.
Wittrock, V.B. & Nordstedt, C.F.O. (1886) Algae aquae dulcis exsiccatae ...