Phylum: Charopyta   Family: Desmidiaceae

Staurodesmus extensus var. joshuae (R. Gutwinski) E. Teiling 1967

First described and illustrated by Gutwinski (1891: 64, pl. 3: 6) as Arthrodesmus incus var. joshuae. It was later moved to its current genus by Teiling (1967: 515, pl. 5: 22-23; pl. 6: 2-3). Differs from the nominate variety in having longer spines which are either parallel or convergent.
Cell dimensions: L: 21-23 µm; B: 22-24 µm; Is: 6-7 µm; Sp: 9-13 µm; Overall B: c.48.
Found in acidic moorland pools and Sphagnum bogs. The scarcest of the varieties and of little-known status in the Outer Hebrides.

References: 
Coesel, P.F.M. & Meesters, K.J. (2023 second edition). Desmids of the Lowlands.
Gutwinski, R. (1892). Flora glonów okolic Lwowa.
Teiling, E. (1967). The desmid genus Staurodesmus. A taxonomic study.