Defien symmetry and describe various types of symmetry found in animals.

Explanation

The arrangement or repetition of similar parts of body is called symmetry. The animals which do not have similarity in parts or arrangement of parts are called asymmetric. Animals having symmetry are called symmetrical. Symmetry is of four types :
(i) Spherical symmetry : The body is like a globe where two equal halves will be formed by any plane of division through the centre. Examples : Volvox, some corals.
(ii) Radial symmetry: The body is cylindrical with equivalent parts being present around a common central axis. The body is divisible into two equal halves by any vertical plane passing through the central axis from top to bottom. Example : Many sponges, coelenterates and echinoderms.
(iii) Biradial symmetry : It is radial symmetry where the body can be divided into two equal parts by only one or two vertical planes. Examples : Sea anemones, comb jellies, star fish.
(iv) Bilateral symmetry : The body is divisible into two equal halves by single plane. The organs of the body are generally paired and arranged around the central axis. Examples : Platyhelminthes, aschelminthes, annelids, arthropods, molluscs and chordates.