elegans (Roy & Bisset) West & G.S.West 1908[2] (syn.

C. elegans) Euastrum tetragonum Nägeli Cosmarium tetragonum is a species of green algae in the family Desmidiaceae.

It is a freshwater species with a worldwide distribution.

Semicells are roughly rectangular in outline, with undulate margins; each side has about four bumps and the top side has about two bumps.

[3] Cosmarium tetragonum is variable and several varieties have been described.