Class 9
Chapter 7 Class 9 - Diversity In Living Organisms
  • These animals have a true vertebral column and internal skeleton.
  • The epidermis is multi-layered.
  • Vertebrates are bilaterally symmetrical, triploblastic, coelomic and segmented, with complex differentiation of body tissues and organs.
  • The heart is three or four-chambered.
  • They have well-developed respiratory and excretory system.
  • Endocrine glands are present in all.
  • All chordates possess the following features:
    1. have a notochord
    2. have a dorsal nerve cord
    3. are triploblastic
    4. have paired gill pouches
    5. are coelomate.


  • Cyclostomes are jawless vertebrates.
  • They are found in aquatic, marine and fresh water.
  • They are characterised by having an elongated eel-like body , circular mouth, slimy skin.
  • They are scaleless.
  • They are ectoparasites or borers of other vertebrates.
  • Single and median nostril is present.
  • They have two-chambered heart.

For Example: Petromyzon(Lamprey) and Myxine(Hagfish)



  • These are fish. They are exclusively aquatic animals.
  • Their skin is covered with scales/ plates.
  • These are cold-blooded organisms.
  • Fertilization may be external or internal.
  • The body is usually streamlined . Some have a spindle-shaped or elongated body as well.
  • They swim with the help of their tail.
  • They obtain oxygen dissolved in water by using gills.

For Example: Synchiropus splendidus(Mandarin fish), Caulophyryne jordani (Angler fish), Scoliodon (Dog fish).



  • Amphibians are found both in water and on land.
  • These animals differ from the fish in the lack of scales, in having mucus glands in the skin, and a three-chambered heart.
  •  Respiration is through either gills or lungs. 
  • They lay eggs.
  • Their body is divided into head and trunk. The tail may or may not be present.
  • They have two pairs of limbs for locomotion.
  • They excrete either ammonia or urea.

For Example: Frogs, toads and salamanders



  • These animals are cold-blooded and have scales.
  • Most of them have a three-chambered heart but crocodiles have four heart chambers.
  • They lay eggs with tough coverings and do not need to lay their eggs in water.
  • Body varies in form and is usually divided into head, neck, trunk and tail.
  • Teeth are present in all reptiles except in tortoise and turtles.
  • Respiration is through lungs only. No gills are present.
  • Fertilization is internal.

For Example: Snakes, turtles, lizards and crocodiles



  • Birds are warm-blooded animals.
  • A toothless beak is present.
  • They have a four-chambered heart with two auricles and two ventricles.
  • They lay eggs. 
  • There is an outside covering of feathers , and two forelimbs are modified for flight.
  • They breathe through lungs. 
  • All birds fall in this category. 
  • Size ranges from smallest humming bird to largest ostrich.
  • Birds have highly developed voice, hearing and vision. They also have specialized sense for nest building and caring for the young.
  • Fertilization is internal. They are oviparous and lay large, yolk-laden eggs having hard shell.

For Example: All birds like crow, sparrow, ostrich, pigeon etc.



  • They are warm-blooded , breath through their lungs and have a four-chambered heart.
  • Their skin is soft, slimy, smooth and scaleless.
  • Respiration is through gills contained in pouches.
  • Presence of hair on their body, sweat and oil glands are exclusive characters of mammals.
  • Presence of pinna i.e external ear is also seen only in mammals.
  • They also have mammary glands to feed their young ones.
  • They usually give birth to live young ones.

For Example: Cat, Rat, Whale, human beings, Rabbit, dog



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CA Maninder Singh is a Chartered Accountant for the past 14 years and a teacher from the past 18 years. He teaches Science, Economics, Accounting and English at Teachoo