polymorphism.pptx

it is the phenomena of the phylum coelentreta.
teo stages of this phenomena are hear discussed.

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.

4. Modification of polyps A) G astrozooids or feeding polyps are concerned with feeding having a mouth and a long tentacle. B) D actylozooids or protective polyp are concerned with protection having no mouth but have a long basal tentacle and having batteries of nematocysts. C) G onazooids 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.

5. 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.

6. 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) G astrozooids or Hydranths. b) G onazooids or B lastostyles. 2] Trimorphic: -They have only three types of zooids and hence the name trimorphic. a) Ga strozooids b) G onazooids c) D actylozooids.

7. 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) G astrozooids b) Spiral dactylozooids c) Long sensory tentaculozooids. d) Skeletozooids. e) Gonozooids.  

8. 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.

9. -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.

10. 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 : - T his 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.  

11. 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.

12. REFERENCE: - MODERN TEXT BOOK OF ZOOLOGY INVERTEBRATES: R.L.KOTPAL, BIBLIOGRAPHY.

13. Thank you.