The property by which an imaginary line or lines can divide an animal into two or more equal halves is called
Symmetry
The property by which an imaginary plane or planes can divide an animal into two or more equal halves is called symmetry. When any plane passing through the central axis of the body divides the organism into two identical halves, it is called radial symmetry. Cnidarians, ctenophores and echinoderms have this kind of body plan. Animals in which the body can be divided into identical left and right halves along just one plane, exhibit bilateral symmetry, such as the annelids, arthropods and most chordates.