Polymorphism refers to the existence of different forms or types of individuals in the same species that differ in structure and function. In coelenterates, polymorphism allows for division of labor within colonies. There are two main polymorphic forms - polyps and medusae. Polyps are sessile with a mouth and tentacles, while medusae are motile and umbrella-shaped. Polymorphism ranges from dimorphic with two types of zooids to polymorphic with many types, and provides advantages like improved protection, feeding, and reproduction that increase colony survival.

1. POLYMORPHISM IN COELENTERATES

2. -Occurrence in the same species of more than one type of individual, which differ in the form and function is
known as polymorphism.
-Polymorphism denotes division of labor among the zooids of the individual.
-In coelenterates different individuals get united in the form of a colony and hence polymorphism is a very
important
-Class hydrozoa is the best example of polymorphism.
INTRODUCTION

3. FORMS OF POLYMORPHISM
-Two main forms are included in polymorphism of coelenterate viz., Polyps and medusa
# Polyps:
- A polyp has a tubular body.
- It has a mouth surrounded by tentacles at one end other end is blind and usually attached by a pedal disc
to the substratum.
- They are sessile or sedentary.
# Medusa:
- A medusae has a bowl or umbrella-shaped body.
- -It has marginal tentacles and mouth centrally located on a projection of the lower concave surface .
- -They are motile.

5. Modification of polyps
A) Gastrozooids or feeding polyps are concerned with feeding having a mouth and a long tentacle.
B) Dactylozooids or protective polyp are concerned with protection having no mouth but have a long
basal tentacle and having batteries of nematocysts.
C) Gonazooids or reproductive polyp are concerned with reproduction which produces asexual budding
forming sexual medusa or gonophores.
D) Tentaculozooid with sensory cells.
E) Skeletozooids spiny projections of chitin.

6. Modification of Medusa
A) Nectophore or Nectocalyx or swimming zooid with a muscular bell without manubrium or
tentacle.
B) Pnematophore or Float as a bladder-like medusa filled with secreted gas.
C) Phyllozooids or Bract, usually leaf-like and studded with nematocysts, serving for protection of
other zooids.
D) Gonophore bearing gonads, which may be either male producing sperms or female producing
ova.

7. Patterns of Polymorphism
-Degree of polymorphism varies greatly in different groups of Hydrozoa.
1] Dimorphic:
-Most simple and the common pattern of polymorphism exhibited by most of the hydrozoan colonies.
-Dimorphic polymorphism is exhibited by many hydrozoan colonies like Obelia, Tubularia.
-They have only two types of zooids and hence the name dimorphic. The two types of zooids are-
a) Gastrozooids or Hydranths.
b) Gonazooids or Blastostyles.
2] Trimorphic:
-They have only three types of zooids and hence the name trimorphic.
a) Gastrozooids
b) Gonazooids
c) Dactylozooids.

8. 3] polymorphic:
-Having more than 3 types of zooids individuals
-E.g- a colony of hydractinia consists of 5 types of polyps each assigned with a special function:
a) Gastrozooids
b) Spiral dactylozooids
c) Long sensory tentaculozooids.
d) Skeletozooids.
e) Gonozooids.

9. Polymorphic polyps of Hydractinia, with three of the polyp types shown in a colony and the fourth
polyp type shown detached. (a) gastrozooid; (b) gonozooid; (c) dactylozooid; and (d) tentaculozooid.

10. -Extreme example of polymorphism are seen in pelagic and floating or swimming colonies of the order
Siphonophora.
-In them both polypoid and medusoid forms occur in same colony which are specialized for feeding,
protection, reproduction, swimming or buoyancy, etc.

11. ORIGIN OF POLIMORPHISM
-There are two theories to explain the origin of polymorphism in coelenterates.
Polyorgan theory:
-This theory was proposed by Huxley (1859), Eschscholtz (1829), E. Metschnikoff
(1874), according to which individual of a colony are actually organs of a medusoid
individual, which have multiplied and migrated form their primitive positions to the
current evolved positions.
Polyperson theory:
-This theory was first proposed by Leuckart (1851), Vogt (1848), Gegenbaur (1854) and
Kollikar (1853), according to this theory colony are modified individual which have
changed their structure due to division of labor. They have all modified from the primitive
zooid which was a polyp.

12. Importance of Polymorphism
- Polymorphism is essentially a phenomenon of division of labor.
- Different functions are assigned to different individual, rather than to parts or
organs of one individual.
- Polymorphism gave the colonies competitive edge in protection and food
gathering and eventual survival.
- Thus polyps are concerned with feeding, protection and asexual reproduction,
while medusa are concerned with sexual reproduction.

13. REFERENCE:- MODERNTEXT BOOK OF ZOOLOGY INVERTEBRATES: R.L.KOTPAL,
BIBLIOGRAPHY.