4. Kingdom Animalia - part 03 - Phylum : Cnidaria

 


4. Kingdom Animalia - part 03 - Phylum : Cnidaria


Phylum : Cnidaria


  • e.g. H ydra, Aurelia (Jelly fish), Physalia (Portuguese man-of-war), Adamsia (sea anemone), Diploria (Brain coral), Gorgonia (sea fan).
  • They are aquatic, mostly marine and few are fresh water forms. 
  • They are sessile or free swimming. 
  • They show radial symmetry and are diploblastic with blind-sac body plan. 
  • Animals exhibit two body forms. Polyp is cylindrical form (Hydra) and medusa is umbrella-like (Aurelia - Jelly fish).
  • Body cavity is meant for circulation as well as digestion. Hence called gastrovascular cavity or coelenteron. 
  • Tentacles bear cnidoblasts or stinging cells which are meant for anchorage, offence and defence. 
  • Cnidarians reproduce both asexually and sexually. 
  • Asexually reproduction takes place by budding and regeneration.
  • Sexual reproduction takes place by gamete formation. 
  • They exhibit alternation of polypoid generation with medusoid generation. This phenomenon is called metagenesis i.e. polyps produce medusae asexually and medusae produce polyps sexually. (e.g. Obelia)

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