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Write five characteristic features of phylum cnidaria? 

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Characteristic features of phylum cnidaria: 

  • Cnidarians are aquatic, sessile or free swimming, solitary or colonial forms 
  • Mostly they are radial symmetry except for sea anemones (bilateral symmetry). 
  • The name Cnidaria is derived from cnidocytes or cnidoblasts with stinging cells or nematocyst on tentacles. 
  • Cnidoblasts are used for anchorage, defense, and to capture the prey.
  • Cnidarians are the first group of animals to exhibit tissue level organisation 
  • They are diploblastic. 
  • They have a central vascular cavity or coelenteron (serves both digestion and circulatory function) with a single opening called mouth or hypostome, which serves the process of ingestion and egestion. Digestion is both extracellular and intracellular. 
  • The nervous system is primitive and is formed of diffused nerve net. 
  • The polyp forms are sessile and cylindrical (Eg: Hydra, Adamsia), whereas the medusa are umbrella shaped and free swimming.
  • Cnidarians which exist in both forms, also exhibit alternation of generations in their life cycle 
  • (Metagenesis). 
  • The polyp represents the asexual generation and Medusa represents the sexual generation.
  •  Polyps produce medusa asexually and medusa forms polyps sexually 
  • Development is indirect and includes a free swimming ciliated planula larva. 
  • Eg: Physalia (Portugese man of war), Adamsia (sea anemone).
  • Cnidarians like corals have a skeleton made up of calcium carbonate. 
  • Cnidarians exhibit two basic body forms, polyp, and Medusa

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