Ex

  Biology (NTSE/Olympiad)  

4. Diversity In Living Organism

Phylum - Cnidaria (Coelenterata)

Phylum - Cnidaria (Coelenterata) :
Aquatic, mostly marine, a few such as Hydra are fresh water solitary or colonial forms.

Cnidarians or coelenterates are multicellular, diploblastic animals with tissue grade of organisation.
Body shows radial symmetry.

Possese specialized cells (cnidoblasts) bearing stinging organoids called nematocysts. Nematocysts serve the functions of paralysing the prey by injecting poison or to hold the prey.
Exhibit the phenomenon of polymorphism (Ex- Physalia).
Body shows two main forms, the polyps and the medusae.
Examples - Hydra, Obelia (sea fur) , Aurelia(jelly fish), Metridium (sea anemone).

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