This phenomenon is called rphism is very common in coelenterates and the class Hydrozoa provides the best example of polymorp. 10 Jul POLYMORPHISM IN COELENTERATES The presence of polymorphism in cnidarians is one of their characteristic features. It is defined as. In Hydrozoan coelenterates polymorphic tendency is well developed. The order Siphonophora organisms are exhibiting this tendency to a maximum extent.

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Cnidarian sexual reproduction often involves a complex life cycle with both polyp and medusa stages. It has mouth at its apex.

Most of their bodies are innervated by decentralized nerve nets that control their swimming musculature and connect with sensory structures, though each clade has slightly different structures.

Nematoda roundworms Nematomorpha horsehair worms. This improves respiration after feeding and allows these animals, which use the cavity as a hydrostatic skeletonto control the water pressure in the cavity without expelling undigested food. Coelenterate animals may show a number of zooids. Hydrozoa Hydrasiphonophorescoelenterated. The class Hydrozoa of polymoprhism Coelenterata includes a large number of colonial species that contain more than one form of individuals which are called zooids.

From its base along tentacle will arise.

Anybody can ask a question Anybody can answer The best answers are voted up and rise to the top. According to this theory, a polymorphic coelenterate is supposed to be a colonial form in which various types of zooids have been aggregated to perform different functions. The circulation of nutrients is driven by water currents produced by cilia in the gastroderm or by muscular movements or both, so that nutrients reach all parts of the digestive cavity.

Polypoid generation absent or represented by small polyp, the scyphistoma which gives rise to medusae by strobilisation or transverse fission. Phyllozooid or bract, usually leaf-like and studded with nematocysts, serving for protection of other zooids.


Coelenterata or Cnidaria are radially symmetrical diploblastic animals with only epidermis and gastrodermis, between these two layers is a jelly-like mesogloea which is originally structure less but in higher forms, it becomes fibrous and has wandering amoebocytes. Polymorphism is, no doubt, a phenomenon of division of labour, i.

Most species have ocelli “simple eyes”which can detect sources of light. Jellyfish Phyllorhiza punctata Scyphozoa. Indigestible remains of prey are expelled through the mouth. Kinorhyncha mud dragons Priapulida penis worms. Submerged bank theory This theory states that both barrier reefs and atolls grew upon pre-existing flat surfaces.

They are called’ Feelers’ or Palpons. All cnidarians can regenerateallowing them to recover from injury and to reproduce asexually. The occurrence of more than one type of structurally and functionally different individuals within a population is called polymorphism.

Cycliophora Symbion Annelida ringed worms. The exoskeleton of a polyp is called a corallite, and the exoskeleton of the colony is a corallum.

Polymorphism in Coelenterata | Zoology and Entomology articles. IAS Zoology.

Fringing reefs are developed in shallow waters on or near the shores of the volcanic islands. The muscular system of the medusa is highly developed because the muscular portion of epitheliomuscular cells increases to form elongated striated muscle fibres and the epithelial part diminishes. Journal of the Geological Society. This is the most simplest and the common pattern of polymorphism exhibited by most of the hydrozoan colonies. The pneumatophore is large and circular.

Coelenterata: General Characters, Tissues and Corals | Metazoa

The phenomenon of polymorphism is essentially one of division of labour in which specific functions are assigned to different individuals. It is difficult to study the firing mechanisms of cnidocytes as these structures are small but very complex.

Like sponges and ctenophores, cnidarians have two main layers of cells that sandwich a middle layer of jelly-like material, which is called the mesoglea in cnidarians; more complex animals have three main cell layers and no intermediate jelly-like layer. Proceedings of the National Academy of Sciences. The epidermal lining becomes glandular to form a gas gland.


This is the most disputable thought about the origin of polymorphism.

Posted by Zoologists at Register and Get connected with Biology experts faculty. What is the difference between Streptoline nematocyst and stereoline nematocyst?

This occurrence of polymorphism guarantees well-organized division of labor between several individuals. The body wall of all the coelenterates contains special defensive structures called as stinging cells or nematocysts.

The nutritive polyps are called gastro zooids.


Nervous system consists of one or more networks or nerve-cells and neurites located in the ectoderm and endoderm.

It is widely distributed on coral reefs. Such a colony is called ‘Polymorphic’ colony. With the help of the polymorpihsm the colony floats on the water. Most Cnidarians also have a parallel system. A polymorphic colony contains many individuals called zooids.

Once the food is in the digestive cavity, gland cells in the gastroderm release enzymes that reduce the prey to slurry, usually within a few hours. Some Anthozoa have ciliated grooves on their tentacles, allowing them to pump water out of and into the digestive cavity without opening the mouth. By studying the lines of growth on the fossils of some mollusk help in knowing about the seasonal fluctuations as the thickness of the growth line varies from season to season. Most have fringes of tentacles equipped with cnidocytes around their edges, and medusae generally have an inner ring of tentacles around the mouth.

Different functions are assigned to different individuals rather than different parts or organs of the body of the same individual.