Phalansterium

Phalansterium is a genus of single-celled flagellated organisms comprising several species, which form colonies. It is the only genus in the family Phalansteriidae. 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.