Animal Kingdom - Notes | Class 11 | Part 13: Chordata (Cyclostomata, Pisces)


  • All are ectoparasites on some fishes.
  • Elongated body without scales and paired fins.
  • 6-15 pairs of gill slits for respiration.
  • Sucking and circular mouth without jaws.
  • Cartilaginous cranium and vertebral column.
  • Circulation is closed type.
  • Marine, but migrate for spawning to fresh water. After spawning, they die. Their larvae, after metamorphosis, return to ocean.
  • E.g. Petromyzon (Lamprey) and Myxine (Hagfish).


Class Chondricthyes (Cartilaginous fishes)

  • Marine. Stream-lined body. Predaceous.

  • Cartilaginous endoskeleton.

  • Notochord is persistent throughout life.

  • Ventral mouth.

  • Gill slits without operculum. Powerful jaws.

  • Skin with placoid scales. Teeth are modified placoid scales which are backwardly directed.

  • No air bladder. So, they have to swim constantly to avoid sinking.

  • Poikilotherms (Cold-blooded animals): Animals that lack the capacity to regulate their body temperature.

  • Two-chambered heart (one auricle and one ventricle).

  • Sexes are separate. In males, pelvic fins bear claspers. Internal fertilization. Many of them viviparous.

  • Scoliodon (Dogfish)

  • Pristis (Saw fish)

  • Carcharodon (Great white shark)

  • Trygon (Sting ray- has poison sting)

  • Torpedo (Electric ray- has electric organ).

Class Osteichthyes (Bony fishes)

  • Marine & fresh water. Stream-lined body.

  • Bony endoskeleton.

  • Terminal mouth.

  • 4 pairs of gills covered by operculum on each side.

  • Scales are Cycloid, ctenoid etc.

  • Air bladder for buoyancy.

  • Poikilotherms (cold-blooded).

  • Two-chambered heart (one auricle and one ventricle).

  • Sexes are separate. External fertilisation.

  • Mostly oviparous. Development is direct.

  • Marine: Exocoetus (flying fish), Hippocampus (seahorse)

  • Fresh water: Labeo (Rohu), Catla (Katla), Clarias (Magur).

  • Aquarium: Betta (Fighting fish), Pterophyllum (Angel fish).

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