Metazoan Branches

The Kingdom Animalia comprises all the multicellular animals (metazoans). These are divided into three branches:

1. Mesozoa
2. Parazoa
3. Eumetazoa

The Mesozoa comprise a tiny single phylum (Phylum Mesozoa); the Parazoa comprise two phyla a tiny single phylum Placozoa and the rest make up the phylum Porifera comprising the sponges. Most of the metazoans come under the major branch Eumetazoa You must note that the cellular layers of Porifera (sponges) are not homologous to the germ layers of Eumetazoa. Their developmental pattern is also quite different from that of the Eumetazoa. The Parazoa are regarded as an early evolutionary side branch of the animal kingdom, which did not give rise to any other group of animals.