Phylum: Charophyta   Family: Desmidiaceae

Hyalotheca mucosa J. Ralfs 1848

First described and illustrated by Ralfs 1848: 53, pl. 1: 2). Cells quadrangular, about as long as broad, each semicell with two parallel rings of tiny granules just beneath the apex. Chloroplast axile with one pyrenoid.
Cell dimensions: L: 15-22 µm; B: 16-22 µm; L/B: 0.80-1.30.
West, West & Carter (1923: 235) record it as neither common or abundant but generally distributed. This is the current situation in the Outer Hebrides. Found in mesotrophic waters, which are slightly acidic.

References: 
Coesel, P.F.M. & Meesters, K.J. (2023 second edition) Desmids of the Lowlands.
Ralfs, J. (1848) The British Desmidieae.
West, W., West, G.S. & Carter, N. (1923) A Monograph of the British Desmidiaceae, Volume 5.