[1][2][3] Tetrabaena socialis is colonial species consisting of four cells.

[2][3] It primarily occurs in freshwater, although it has been found in saltwater on at least one occasion.

[3] Tetrabaena socialis is a member of the order Chlamydomonadales, a model lineage used in the study of the origins of multicellular organisms from single celled ancestors.

[2][3] Within Chlamydomonadales, it is notable for being the colonial species with the smallest number of cells (4), placing it at the boundary between single- and multi-cellularity.

As such, it has been characterized as the "simplest integrated multicellular organism.