Division Gnathostomata

The animals possess jaws and paired lateral appendages. The group is divided into 7 classes.

  1. Class Placodermi (extinct)
  2. Class Chondrichthyes
  3. Class Osteichthyes
  4. Class Amphibia
  5. Class Reptilia
  6. Class Aves
  7. Class Mammalia


Class : Chondrichthyes

Class Chondrichthyes (Chondros – cartilage; ichthys – fish) consists of fishes with cartilagenous endoskeleton.

Habitat: All members are marine. These animals are mostly predaceous.


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(Dog fish),


(Saw fish)

Carcharodon (Great white shark) Trygon

(Sting ray)

Body characteristics:

  • All the members have streamlined body and a cartilagenous endoskeleton. Fins also have cartilaginous rays.
  • Mouth is present in the ventral surface.
  • Five to seven pairs of gills are present. Gill slits are separate. They do not have an operculum (gill cover).
  • The skin is tough, containing minute placoid scales.
  • Teeth are modified placoid scales which are backwardly directed.
  • Their jaws are very powerful.
  • Heart is two-chambered (one auricle and one ventricle).
  • They possess lateral line sense organs. Some of them have electric organs (e.g., Torpedo) and some possess poison sting (e.g., Trygon).



  • Due to the absence of air bladder, they have to swim constantly to avoid sinking.
  • They are cold-blooded (poikilothermous) animals, i.e., they lack the capacity to regulate their body temperature.

Notochord: Notochord is persistent throughout life.

Reproduction: Sexes are separate. In males pelvic fins bear claspers. They have internal fertilisation and many of them are viviparous.


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