Phylum: Charophyta   Family: Desmidiaceae

Cosmarium pygmaeum  W. Archer 1864

Rarely reported but thought to be widespread in association with Sphagnum. Its diminutive size and confusion with similar small species has probably led to under-recording. A characteristic is the asymmetrical disposition of the granules on the upper lateral angles.

References: 
Coesel, P.F.M. & Meesters, K.J. (2007) Mesotaeniaceae and Desmidiaceae of the European Lowlands
John, D.M. & Williamson, D.B. (2009) A Practical Guide to the Desmids of the West of Ireland
Prescott, W.G., et al. (2001 reprint) A Synopsis of North American Desmids. Part II, Desmidiaceae: Placodermae, Section 33