Phalansterium is a genus of single-celled flagellated organisms comprising several species, which form colonies. Phalansterium produces tetraspores.
Phalansterium is hard to classify; it has a distinctive ultrastructure of its pericentriolar material. Molecular evidence places it in the Amoebozoa.
It has been suggested that it is similar to the ancestral eukaryote.
Genus Phalansterium <small>Cienkowsky 1870</small>