SYMMETRY

Asymmetry :
The organisms that lack a particular form or geometrical arrangement of parts and cannot be divided into mirror image halves by any plane are kinown asymmetrical organisms. This phenomenon is called asymmetry. Eg :- Most of the sponges and Amoeba
Spherical symmetry :
1.Body is sphere shaped 2.This symmetry is also called Homaxial apolar symmetry
3.all axes are equal 4.Poles are absent 5.This is suitable for floating and rolling
6.This is rare symmetry Eg :- Heliozoans and Radiolarians
Radial symmetry :
1.The body is cylindrical or Vase-like or Umbrella shaped
2.This symmetry is also called Monaxial heteropolar symmetry 3. Principal axis is oro-aboral axis
4.Poles are different 5.Various body parts are arranged around the principal axis
Eg:- Hydra , Jellyfish
Biradial symmetry :
1.Body is cylindrical
2.Oro-aboral axis is principal axis , along with this long axis and short axis are present
3.Two planes are present 4.Some structures are paired ,some are radially arranged
Eg :- Anthozoans (Sea anemone) , Ctenophores
Bilateral symmetry :
1.Principal and Saggital axis are heteropolar
2.Only median saggital plane is present
3.The appearance of bilateral symmetry was a major advancement in animal evolution
4.Bilateralsymmetry leads to cephalization
5.The organisms exhibiting bilateralsymmetry show quick responses to the external stimuli
Eg :-Triploblastic phyla