Chondrichthyes - The Cartilaginous Fishes (Elasmobranchs)-characteristics

There are about 600 species of cartilaginous fishes. They are all marineorganisms

1. The fishes of this class bear cartilaginous endoskeleton. 

They are cold blooded or ectothermic.

2. The exoskeleton of these fishes consists of placoid scales, which are dermal in origin.

3. Except in the Chimaeras, the gills are not covered by an operculum or gill cover.

4. Jaws are well developed.

 Mouth is ventrally placed. 

A spiral valve called scroll valve isusually present in the intestine. The digestive tract leads into the cloaca.

5. External nares are present on the ventral side of the head and the internal nares are lacking.

6. Paired fins are broad but the he caudal fin is mostly heterocercal.

7. Heart is two chambered  with one auricle and one ventricle . Heart has a well developed with sinus venosus and conus arteriosus. There is well developed renal portal system.

8. Kidneys are mesonephric. Urea is chief nitrogenous waste or ureotelic

9. There have 10 paires of cranial nerves.

10. Lateral line sensory system is well developed.

11. Swim or air bladder is absent in these fishes and they have to swim constantly else

  they will sink to the bottom.

12. They have cloaca. Male usually has claspers which are used in copulation. 

The fertilization is internal.

Examplesz. Scoliodon-Dog fish, Sphyrna-Hammer headed shark, Pristis-Jaw fish,

Torpedo-Electric ray, Trygon-Sting ray, Chimaera-Rat or Rabbit fish or king of

herrings, Stegostoma-Zebra (Tiger) fish, Rhinobates-Guitar fish, Chimaera-Rat fish,

Rhinodon (21 m)-Largest fish, Whale shark, Carcharodon- Great white shark.

Scoliodon (Dog fish)