What is "desmidian"

Desmid \Des"mid\, Desmidian \Des*mid"i*an\, n. [Gr. desmo`s chain + e'i^dos form.] (Bot.) A microscopic plant of the family Desmidi[ae], a group of unicellular alg[ae] in which the species have a greenish color, and the cells generally appear as if they consisted of two coalescing halves.