General Characteristics and Classification of Cnidaria
A brief introduction to phylum Cnidaria Phylum Cnidaria (also called as coelenterata) includes about 9000 species. Some are found in fresh water, but the greater numbers are in marines. Coelenterates (Greek word. koilos- hollow + enterongut) are the simplest of eumetazoans. .They include the hydra, jellyfish, sea anemones and corals. GENERAL CHARACTERS- 1. Cnidarians are multicellular animals with tissue grade of organisation. 2.Body radial or bi-radially symmetrical with oral-aboral axis. 3. They are diploblastic animals. 4. Coelenterate animals are represented by two morphologically different types of individuals, polyps and medusa. 5. Polyps are sessile/stationary (attached to the substratum) with a tubular body (eg. Hydra). Whereas medusa are free-swimming with an umbrella or bell-shaped body, eg. Aurelia, Metridium. 6. They are all aquatic, mostly marine and some freshwater (eg. Hydra). 7. They may exhib...