Types of animals on the basis of symmetry - 1. Asymmetrical - No particular symmetry. Examples : Most of sponges. 2. Radially symmetrical - When any plane passing through the central axis of the body divides the organism in 2 equal halves. Examples : Few sponges, coelenterates, ctenophores and adult echinodermates. 3. Bilaterally symmetrical - Body of organism is divisible into 2 equal halves only in one plane. Examples : Platyhelminthes, aschelminthes, annelids, arthropods, molluscs, echinodermates and chordates.