Phylum: Charophyta   Family: Desmidiaceae

Sphaerozosma vertebratum J. Ralfs 1848

First described and illustrated in Ralfs (1848: 65, pl. 6: 1). West & West (1897: 497, pl. 6: 7) described and illustrated a variety latius having broader cells but as intermediate occur, it has been absorbed into the nominate variety. Specimens with these broader cells are very similar to S. aubertianum West (1889: 206, pl. 291: 17), which has a more open sinus and a zygospore that is furnished with long spines. The spores, illustrated by Ralfs (1848, pl. 32: 2) for the nominate variety, are smooth.
Cell dimensions: L: 12-20 µm; B: 15-29 µm; Is: 10-11.5 µm; L/B: 0.66-1.00.
Possibly a northern European distribution, found in mesotrophic habitats such as moorland pools and acidic bogs. Infrequently recorded in the Outer Hebrides.

References: 
Coesel, P.F.M. & Meesters, K.J. (2023 second edition) Desmids of the Lowlands.
Ralfs, J. (1848) The British Desmidieae.
West, W. (1889) The freshwater algae of Maine.
West, W. & West, G.S. (1897) A contribution to the freshwater algae of the south of England.