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Thursday, October 1, 2020

Class Chondrichthyans - NEET - Biology

Class Chondrichthyans

Fig: Rhinocodon

  • They have a skeleton that is composed predominantly of cartilage, often impregnated with calcium.

Important characteristics:

  • Marine animals having cartilaginous endoskeleton.
  • The notochord is persistent throughout life.
  • Gill slits are separate & operculum (gill cover) is not present.
  • The skin is tough, containing minute placoid scales.
  • The stomach is J-shaped.
  • The swim bladder & lungs are absent and the liver is filled with oil to provide buoyancy to the body while swimming.
  • Due to the absence of an air bladder (fish maw), they have to swim constantly to avoid sinking. If they stop swimming, they will sink (fall) like a stone.
  • The heart is two-chambered (one auricle & one ventricle).
  • Kidneys opisthonephric. Excretion ureotelic. Cloaca present.
  • Fertilization is external. Sexes are separate.
  • The pectoral fins of the shark are called claspers & used for copulation.
There are three ways in which sharks reproduce;
  • Oviparous= in which the female lays eggs which takes a few months to develop.
  • Ovoviviparous= where the eggs are hatched in the oviduct & the embryo develops in the uterus.
  • Viviparous= in which the gestation period of the embryo is about one year.
Examples: Rhinocodon (whale shark), Carcharodon (great white shark), Trygon (stingrays), Torpedo (electric rays), Scoliodon (dogfish), Pristis (sawfish).
Fig: Stingrays



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