Polymorphism of Cnideria

Introduction :- 

Polymorphism is a phenomenon of existance of different physiological and morphological forms represented by an extensive range of variations.
To define in other way, polymorphism means the existance of individuals(zooids) of a single species in more than one forms and functions.

Theories of Polymorphism :- 

Various theories have been put forward to explain the phenomenon of polymorphism, of these the important theories are-

(i) Poly Organ Theory :- 

Huxley & other suggested that each polymorphic is an individual member, of which polyp & medusa budded of as organ.

(ii) PolyPesson Theory :-  

This theory suggest that the cniderian colony is made up of independent & separate individuals which remain inorganic connections, with one another. This theory hold that zooids are separate individuals.

(iii) Medusa Theory :- 

This theory advocates that primitive zooids of the polymorphic colony was a Medusa which produce other Medusa by budding. Medusa possess locomotary and reproductive power. This theory holds that different organs of the colony are nothing but to time from their attachment.

(iv) Neoteny Theory :- 

Polymorphic colony arrows by neoteny and having the power of reproduction in larval conditions and there by specialization of zooids takes place.

Significance of Polymorphism :-

(i) Division of labour (function) due to lack of organs and low level of organization. Polyp zooids are concerned with food capture, feeding, nutrition, respiration, excretion, asexual reproduction etc.

and medusoid zooids are involved with sexual reproduction, protection, floating etc.

(ii) For more security, food gathering & distribution of individual.

(iii) Due to metagenesis i,e alternation of sexual & asexual stages of life cycle enhance the survival & rejuvenation of genetic materials.

       Polymorphism is the most characteristic feature of colonial Cniderians. Entire polymorphic diversities present in a species of colonial cniderians can be reduced into two zooids the polyp & medusa, which remain in organic connection with one another.

In the class Hydrozoa polypoid & medusoid forms is predominant while in class Actinozoa, zooids are exclusively polypoid. Extreme specialization of forms is exhibited by the members of the order Siphonophora of the class Hydrozoa. Their colonies exhibit highest degree of Polymorphism.