Polyphyletic Theory - Metazoa

This theory was suggested by Greenheig (1959) and some other workers. According to this theory, sponges, coelenterates, ctenophores and flatworms have each evolved independently from protozoans. Sponges and coelenterates have probably arisen through colonial flagellates, while ctenophores and flatworms through ciliates or even mesozoans.

It is apparent that this theory is a compromise between the Syncytial and colonial theory.