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Animal Kingdom – Chordates

by Ramneet Kaur


  1. Characteristics of primary chordates:
  • Notochord: hard rod like endoskeletal structure present on the dorsal side.
  • Nerve chord.
  • Pharyngeal gill slits: found in primitive chordates.
  1. Characteristics of secondary chordates:
  • Bilaterally symmetrical.
  • Triploblastic coelomates.
  • Organ-system level of organization.
  • Closed circulatory system.
  • Ventral heart.
  • Post-anal tail supported by a notochord.



Notochord changes into bony or cartilaginous vertebral column.

  • They have a ventral muscular heart with 2, 3 or 4 chambers.
  • Kidneys for excretion and osmoregulation.
  • Paired appendages as fins or limbs.
  • Sexes are separate.
  • Closed circulatory system.


  • They are ectoparasites on some fishes.
  • Have an elongated body, having 6 – 15 pairs of gill slits for respiration.
  • Mouth is circular and sucking without jaws.
  • The body is devoid of scales and paired fins.
  • Cyclostomes are marine but migrate for spawning to fresh water. (Anadromous).

Pisces: (fishes)

  • Streamlined body.
  • Heart 2- chambered, single circulation, heart have veins to gills, only blood.
  • Cold blooded animals / poikilothermal / ectotherms.
  • Development is direct.

 Endoskeleton Cartilaginous Bony
 Mouth Ventral Terminal
 Gills 5-6 pairs,

no operculum

 4 pairs,

operculum present

 Scales Placoid Cycloid/ctenoid
 Air bladder Absent, so they swim      continuously Present
 Caudal fin Heterocercal Homocercal
 Fertilization Internal External
 Reproduction Viviparous Oviparous


  • Some have electric organs e.g., Torpedo and some have poison sting e.g., Trygon.
  • Male’s pelvic fins bear claspers.


  • Can live in both aquatic & terrestrial environment.
  • The body is divided into head & trunk, some have a tail.


  • They are creeping or crawling animals.
  • Snakes & lizards show ecdysis.

Aves (birds):

  • Streamlined body, feathers present.
  • Jaw is modified into beak.
  • Hind-limbs generally have scales modified for walking, swimming & clasping.
  • Oil glands at the base of the tail.
  • Bones are fully ossified and pneumatic (hollow, having air cavity).
  • Digestive structure has additional chambers, the crop & gizzard.


  • Unique characterstic is presence of mammary glands.
  • Teeth is heterodont, thecodont & diphyodont.
 Moist without  scales Dry, covered with  scales/scutesDry, covered with  feathers & scales  on legs Body hair, oil &  sweat glands  present
 2 pairs, webbed  feet 2 pairs Forelimbs  modified into wings, hind limbs  present 2 pairs
 3 – chambered 3 – chambered, 4  in crocodile 4 – chambered 4 – chambered
 Tympanum  presentTympanum present Ear opening  present External ear with  pinna
 Gills, lungs &  skinLungs Lungs with air sacs connected Lungs
 Body        temperature
 Cold blooded Cold blooded Warm-blooded Warm-blooded
 UreotelicUricotelic/ureotelic Uricotelic Ureotelic
 Cranial    nerves
 10 pairs12 pairs12 pairs12 pairs
 External Internal Internal Internal
 Indirect Direct Direct Direct
 Oviparous Oviparous, Macrolecithal eggs Oviparous,  Macrolecithal &  calcareous eggs Viviparous,  except Platypus.

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