Class Chondrichthyans - NEET - Biology

Class Chondrichthyans

Fig: Rhinocodon

• Chondrichthyans = cartilage fish.

• 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 mouth is located ventrally. Jaws are present. Teeth are modified 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.

• They are cold-blooded animals, i.e. they are incapable to regulate their body temperature. They do not maintain constant body temperature. They get their heat from the outer environment.

• 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