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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Polymorphism in Coelenterata

Ichthyosporea Pluriformea Syssomonas Corallochytrea. In Siphonophora many examples can explain polymorphic tendency. Such a colony is called ‘Polymorphic’ colony.

Some of them grow into huge mounds, while others are large and branched colonies. Physalia is commonly known as Portuguese man of war. The chief type of cell found in lower Coelenterata is a columnar epitheliomuscular cell produced into muscle fibres which are embedded in the mesogloea. Coral reefs form some of the world’s most productive ecosystems. In scyphozoans, this takes the form of a diffuse nerve net, which has modulatory effects on the nervous system.

Anthozoan larvae either have large yolks or are capable of feeding on planktonand some already have endosymbiotic algae that help to feed them. Gastrozooids for feeding 2. Polymorphism is, no doubt, a phenomenon of division of labour, i.

Each cnidocyte contains a fluid filled membranous capsule called cnida. Dimorphic polymorphism is exhibited by many hydrozoan colonies like Obelia, Tubularia. There is an oval ciliated planula larva during development. They are of different forms. Sea fan Gorgonia ventalina Alcyonaceapart of Octocorallia. Most Hydrozoa colenterates dimorphism, there is a nutritive polyp or gastrozooid which is sessile, it has a mouth, tentacles and an enteron cavity for food.


They are also known as hydranths Gonozooids are concerned with asexual reproduction.

coelenteraates This page was last edited on 8 Novemberat They are also known as coelentrates Trimorphic: Hydra and most sea anemones close their mouths when they are not feeding, and the water in polymotphism digestive cavity then acts as a hydrostatic skeletonrather like a water-filled balloon.

These corals are being used in the surgery for bone grafts and jaw surgery etc. It is coeleenterates nutritive zooid. Meanwhile, life cycle reversal, in which polyps are formed directly from medusae without the involvement of sexual reproduction process, was observed in both Hydrozoa Turritopsis dohrnii [26] and Laodicea undulata [27] and Scyphozoa Aurelia sp.

Polymorphic tendency in siphonophora animals The polymorphic tendency reached its peak in coelenterate organisms belonging to order ‘Siphanophora’ of class ‘Hydrozoa’. Zygote develops into a free swimming ciliated planula larva which settles down and metamorphosis into a young coral polyp.

Medusae have limited ability to regenerate, but polyps can do so from small pieces or even collections of separated cells. According to this theory, a polymorphic colony is supposed to be a single medusoid zooid; its various components are regarded to be the modified organs of this medusoid zooid.

These are functionally non-feeding and defensive polyps bearing batteries of nematocysts. Sometimes both fringing reefs and barrier reefs may join each other at the bottom of the sea. Indigestible remains of prey are expelled through the mouth. The enteron is restricted to a central gastric cavity and canals, this is due to an increase in thickness of the mesogloea on the aboral side which pushes the two endoderm layers together to form a double layered endoderm lamella.


Among Octocorallia, Stolonifera includes colonial corals like Tubipora or organ pipe coral. Therefore, they not only help in sexual reproduction but also play an important role in dispersal of the colony. The presence of these defensive structures is one of the most important characteristic features of coelenterates. Cnidarians are distinguished from all other animals by having cnidocytes that fire harpoon like structures and are used mainly to capture prey.

Phylum Cnidaria: Polymorphism and Defense structures | Study&Score

Some species like Obelia and Plumularia are trimorphic because besides gastrozooids and medusa, they also have medusa-producing gonozooids or blastostyle.

Coelenterata are noted for their polymorphism, but the various types are reducible to either a polypoid or medusoid type. Sea anemones Actinariapart of Hexacorallia. When discharged, it tightly coiled round the small projections like hair or bristles of the prey and thus stopping the movement of the prey. They help in studying the evolution of the animals as fossils of the animals are preserved in the coral reefs over the years.

In other the gonozooids may form stalked branches bearing grape like structures called gonophores. Cnidocytes help not coelenteeates in defense but also in ppolymorphism, adhesion and capture of prey.