Symmetry - Metazoa

All living organisms have some body shape and form. The general body plan of animals may be organized in one of several ways . Arrangement of parts or organs on either side of an imaginary dividing line or around a common axis or radially around a point so that opposite parts are mirror images of one another is called symmetry. There are two broad divisions of symmetry,

(i) Primary, or embryonic

(ii) Secondary, or adult.

Figure:  Different types of body symmetries

The latter may or may not be the same as the primary one. For example, the larva of starfish is bilaterally symmetry but the adult starfish is radially symmetrical. The primary symmetry is bilateral and secondary symmetry is radial. With regard to symmetry animals can be basically of five types

• Asymmetrical
• Spherical
• Bilateral
• Radial and
• Biradial