Class 11 Biology Animal Kingdom Phylum Coelenterata (Cnidaria)

Phylum Coelenterata (Cnidaria)

  • The name Cnidaria is derived from the cnidoblasts or cnidocytes , which contain the stinging capsules or nematocytes present on the tentacles and the body.
  • Cnidarians exhibit tissue level of organisation and are diploblastic, digestion is extracellular and intracellular, and have a central gastro-vascular cavity with a single opening, hypostome.
  • Cnidarians like corals have a skeleton composed of calcium carbonate and exhibit two basic body forms called polyp and medusa, polyp is sessile and cylindrical form like Hydra, whereas, the latter is umbrella-shaped and free-swimming like Aurelia.
  • Cnidarian which exist in both polyp and medusa forms exhibit alternation of generation called as
  • Polyps produce medusae asexually and medusae form the polyps sexually (e.g., Obelia).

Examples- Physalia (Portuguese man-of-war), Adamsia (Sea anemone).


Fig. Sea anemone

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