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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Register and Get connected with Polumorphism experts faculty. It shows great variation in its structure and size in different siphonophores. They are usually carnivorous; digestion is extracellular as well as intracellular. The polyp leads an easy i life, it has a fixed cylindrical body with a comparatively thin body wall, the free distal end has a hypostome with an apical mouth leading into an enteron, below the hypostome is a circle of extensible tentacles directed upwards coelenteraets armed with nematocysts, the tentacles may be hollow containing an extension of the enteron, the proximal end of the polyp is closed.

Other end is blind and usually attached by a pedal disc to the substratum. Polyp and medusa are in fact homologous structures and from one another can easily be derived.

According to them the indivldualsof the colony are the organs of a single medusoid individual i. In Diphyes colonies are linear with one or more nectophores located at the apical end. They exhibit the phenomenon of polymorphism with very few exceptions; the main types of zooids in polymorphic forms are polyps and medusa. It shows batteries of nematocysts. Finally, Leuckart separated the coelenterates from echinoderms and created a separate phylum Coelenterata Gr.

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In order Siphonophorasuch as Diphyes, Halistemmia, Stephalia and Physalia, zooids are so much modified that they appear like organs of a single body rather than individuals polymorpjism a colony.

They feed at night both by raptorial and suspension feeding. Staurozoa have recently been recognised as a class in their own right rather than a sub-group of Scyphozoa, and the parasitic Myxozoa and Polypodiozoa are now recognized as highly derived cnidarians rather than more closely related to the bilaterians.

Polymorphism in Coelenterata

It produces sexual medusa form. The epidermal lining becomes glandular to form a gas gland.

Echinodermata starfish and relatives Hemichordata acorn worms pterobranchs. Tentacles simple, rarely branched hollow cone-shaped, numerous arranged in the multiple of five and six but never eight. Common coral reef cnidarians include both Anthozoans hard corals, octocorals, anemones and Hydrozoans fire corals, lace corals. Coe,enterates have only two types of zooids and hence the name dimorphic. On the rim or margin of the disc a number of tentaculozooids are present.

Now as a result the operculum is forced to open up, then the coiled thread tube turns inside out and finally the whole nematocyst explodes to the outside. The Anatomical Record Part A: It gave rise to hydroid colony by asexual budding. The thread tube once discharged cannot be withdrawn in other words; the nematocyst once exploded cannot be used again.

They may resemble gastrozooids having mouth but are without tentacles and bear medusa.

The lower end of the colony usually consists of a basal plate for the attachment with some objects. Endoskeleton is the product of mesogleal cells comprised calcareous spicules either calcareous or horny in nature. Three types of cnidocytes are known: The main waste product of cells’ internal processes is ammoniawhich is removed by the external and internal water currents.


This grouping of Cnidaria and Bilateria has been labelled ” Planulozoa ” because it suggests that the earliest Bilateria were similar to the planula larvae of Cnidaria. Jellyfish Phyllorhiza punctata Scyphozoa. Proceedings of the National Academy of Sciences.

These are mainly useful in attachment and to impede the movement of small animals.

Biology – Phylum-Coelenterata | askIITians

These mass spawnings may produce hybridssome of which can settle and form polyps, but it is not known how long these can survive. Click here for study material on Animal Kingdom. Holomycota Cristidiscoidea Zoosporia Opisthosporidia True fungi. The gas gland secretes gas into the air-sac.

Tubipora is commonly known as organ pipe coral. Cnidarians were for a long time grouped with Ctenophores in the phylum Coelenteratacoelenteratez increasing awareness of their differences caused them to be placed in separate phyla. Modifications of Medusa forms Nectophore also called as swimming zooid. The polyp and medusa occur in a number of morphological variations.

A few polyps collect materials such as sand grains and shell fragments, which they attach to their outsides. Their bodies consist of mesogleaa non-living jelly-like substance, sandwiched between two layers of epithelium that are mostly one cell thick. Origin of polymorphism Colonies of the order Siphonophora shows the highest degree of polymorphism showing greatest number of polyp and medusa forms.

University of California Museum of Paleontology. The mesoglea contains small numbers of amoeba -like cells, [10] and muscle cells in some species.