Animal kingdom is divided into two sub-kingdoms, the Parazoa and Eumetazoa based on their organization.
1. Parazoa: These include the multicellular sponges and their cells are loosely aggregated and do not form tissues or organs.
2. Eumetazoa: These include multicellular animals with well defined tissues, which are organised as organs and organ systems.
3. Eumetazoans includes two taxonomic levels called grades. They include Radiata and Bilateria