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Chordate Classes Features ICSE Class 9 Biology Notes

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BiologyICSE Class 9 · Diversity in the Animal Kingdom

Chordates: Fishes, Amphibians, Reptiles, Birds and Mammals (ICSE Class 9 Biology)

Updated 17 October 2026 · Fact-checked

Chordates have a notochord at some stage. The vertebrate classes are Pisces (fishes: gills, fins, scales), Amphibia (moist skin, life on land and water), Reptilia (dry scaly skin, lay eggs on land), Aves (feathers, wings, warm-blooded) and Mammalia (hair, mammary glands, mostly live-bearing).

Understand Chordates: Fishes, Amphibians, Reptiles, Birds and Mammals

1. Chordate characters. A notochord (at some stage), a dorsal hollow nerve cord and gill slits at some stage. In vertebrates the notochord is replaced by a backbone.

2. Pisces (fishes). Aquatic, cold-blooded (poikilothermic), body streamlined with fins and covered with scales, breathe through gills, two-chambered heart, lay eggs. Examples: rohu, shark, sea horse.

3. Amphibia. Live both in water and on land, cold-blooded; moist skin without scales; breathe by gills in the larva and by lungs and skin as adults; three-chambered heart; eggs are laid in water. Examples: frog, toad, salamander. Metamorphosis changes tadpole into adult.

4. Reptilia. Cold-blooded, dry skin covered with scales, breathe by lungs, mostly three-chambered heart (crocodile four), lay shelled eggs on land. Examples: lizard, snake, turtle, crocodile.

5. Aves (birds). Warm-blooded (homeothermic), body covered with feathers, forelimbs modified as wings, beak without teeth, lungs with air sacs, four-chambered heart, lay hard-shelled eggs. Examples: crow, pigeon, ostrich.

6. Mammalia. Warm-blooded, hair on the body, mammary glands that feed the young with milk, external ears (pinnae) in most, four-chambered heart, diaphragm; most are viviparous (give birth to young). Exceptions: the platypus lays eggs. Examples: human, whale, bat, kangaroo.

7. Warm and cold blooded. Warm-blooded animals keep the body temperature almost constant; cold-blooded animals' body temperature changes with the surroundings.

Chordates: Fishes, Amphibians, Reptiles, Birds and Mammals: key facts

Fishes
  • Gills
  • Fins
  • Scales
  • Two-chambered heart
  • Cold-blooded
Amphibians and reptiles
Amphibian: moist skin, metamorphosis | Reptile: dry scales, shelled eggs on land
Birds
  • Feathers
  • Wings
  • Four-chambered heart
  • Warm-blooded
  • Air sacs
Mammals
  • Hair
  • Mammary glands
  • Four-chambered heart
  • Diaphragm
  • Mostly viviparous

Chordates: Fishes, Amphibians, Reptiles, Birds and Mammals in real life

The idea, met in an everyday situation. Answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Winter morning in a pond

Suppose a lizard on a rock, a frog at the pond edge and a crow on a tree all come out on a cold morning; the lizard moves slowly while the crow is active.

Explain the difference in activity.

Try it first, then show the solutionSolution
  1. The lizard is cold-blooded: its body temperature follows its surroundings, so it is slow when cold.
  2. The crow is warm-blooded: its temperature stays steady, so it stays active.

Answer: Cold-blooded reptile and amphibian are sluggish; warm-blooded bird stays active.

Memory hook: Cold body, cold start.

Tricks to remember Chordates: Fishes, Amphibians, Reptiles, Birds and Mammals

Short memory aids. Say each one aloud once, then use it on a question the same day.

  • PARAM

    Pisces, Amphibia, Reptilia, Aves, Mammalia in evolution order.

    Use it when: Class order.

  • Hair + milk

    Hair and mammary glands only in mammals.

    Use it when: Mammal definition.

Chordates: Fishes, Amphibians, Reptiles, Birds and Mammals: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Match · 4 marks · Short answerBoard level

Name the class of (a) frog, (b) crow, (c) whale, (d) snake. [4]

Try it first, then show the solutionSolution
  1. (a) Amphibia.
  2. (b) Aves.
  3. (c) Mammalia.
  4. (d) Reptilia.

Answer: (a) Amphibia (b) Aves (c) Mammalia (d) Reptilia.

Example 2: Amphibia versus Reptilia · 3 marks · Short answerHarder board level

Give three differences between amphibians and reptiles. [3]

Try it first, then show the solutionSolution
  1. Skin: moist and without scales versus dry with scales.
  2. Eggs: laid in water without shell versus laid on land with shell.
  3. Development: metamorphosis versus direct development.

Answer: Amphibians have moist skin, lay eggs in water and show metamorphosis; reptiles have dry scaly skin and lay shelled eggs on land.

Example 3: Whale puzzle · 3 marks · Short answerHarder board level

A whale lives in water and breathes with lungs. Why is it a mammal and not a fish? Give three reasons. [3]

Try it first, then show the solutionSolution
  1. It breathes air through lungs, not gills.
  2. It has mammary glands and suckles its young.
  3. It has hair (few), a four-chambered heart and gives birth to young.

Answer: Because it breathes with lungs, nurses its young with milk and is warm-blooded.

Example 4: Heart and class · 4 marks · Long answerHarder board level

The hearts of four animals have 2, 3, 3 and 4 chambers: fish, frog, lizard, pigeon. (i) Arrange the animals by increasing efficiency. [2] (ii) Why is the four-chambered heart needed in birds and mammals? [2]

Try it first, then show the solutionSolution
  1. (i) Fish (2), frog and lizard (3), pigeon (4).
  2. (ii) Four chambers keep oxygenated and deoxygenated blood separate.
  3. This gives a high oxygen supply for steady body heat and activity.

Answer: (i) Fish, frog, lizard, pigeon (ii) To separate the blood for greater oxygen supply and warm-bloodedness.

Example 5: Exceptions case · 5 marks · Case-basedHOTS / competency

Case. A platypus lays eggs but has hair and feeds its young with milk. (i) Name the class it belongs to. [1] (ii) Which feature decides its class? [1] (iii) Which feature seems to disagree? [1] (iv) Why must classification use many characters? [2]

Try it first, then show the solutionSolution
  1. (i) Mammalia.
  2. (ii) Hair and milk.
  3. (iii) Laying eggs.
  4. (iv) A single character can mislead; several characters together give a reliable class.

Answer: (i) Mammalia (ii) Mammary glands and hair (iii) Egg-laying (iv) Classification relies on a set of characters, not one.

Where students lose marks in Chordates: Fishes, Amphibians, Reptiles, Birds and Mammals

The slips examiners see most often, and what to write instead.

  • Mistake: Writing that fish have lungs

    Gills are the organ.

    Do this: Fish have gills; lungfish are exceptions.

    Usually costs: 1 mark.

  • Mistake: Calling bats birds

    Wings are the only clue.

    Do this: Bats are mammals.

    Usually costs: 1 mark.

  • Mistake: Saying all mammals lay no eggs

    Platypus is an exception.

    Do this: Mention that most are viviparous.

    Usually costs: 1 mark.

Exam tips

  • Memorise skin, breathing, heart and eggs for each class.
  • Tabulate classes with four features.
  • Include an example for every class.
  • Name exceptions only when asked.

Practice questions on Chordates: Fishes, Amphibians, Reptiles, Birds and Mammals

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

  1. Q1 · 1 mark · MCQBoard level

    The scales of a snake are made for:
    (a) swimming
    (b) protection against drying
    (c) flying
    (d) hearing

    Hint

    Dry skin.

    Answer

    (b) protection against drying.

  2. Q2 · 2 marks · Very short answerBoard level

    Name two features of birds that help them fly. [2]

    Hint

    Wings.

    Answer

    Feathers and wings, with lightweight air sacs.

  3. Q3 · 2 marks · Very short answerBoard level

    What is metamorphosis? Give an example. [2]

    Hint

    Tadpole.

    Answer

    Change from a larva to an adult; tadpole to frog.

  4. Q4 · 1 mark · Assertion-reasonHarder board level

    Assertion (A): Frogs lay eggs in water.
    Reason (R): Frog eggs have no hard shell and dry up on land.
    (a) Both A and R are true and R is the correct explanation of A.
    (b) Both A and R are true but R is not the correct explanation of A.
    (c) A is true but R is false.
    (d) A is false but R is true.

    Hint

    Shell.

    Answer

    (a).

  5. Q5 · 3 marks · Short answerBoard level

    State three differences between birds and mammals. [3]

    Hint

    Body cover.

    Answer

    Birds have feathers, lay hard-shelled eggs and have a beak; mammals have hair, mostly give birth and have mammary glands.

  6. Q6 · 3 marks · Short answerHarder board level

    Why are reptiles more successful on land than amphibians? [3]

    Hint

    Dry skin.

    Answer

    Their dry scaly skin reduces water loss, and their shelled eggs can be laid on land.

  7. Q7 · 2 marks · Very short answerHarder board level

    A bat flies but is not a bird. Give two features to prove it. [2]

    Hint

    Fur.

    Answer

    It has hair and mammary glands and gives birth to young.

  8. Q8 · 3 marks · Short answerHarder board level

    Explain why a fish dies out of water but a frog does not. [3]

    Hint

    Breathing.

    Answer

    A fish breathes only through gills; a frog has lungs and a moist skin that lets it breathe on land.

  9. Q9 · 4 marks · Case-basedHOTS / competency

    Case. Given: animal X has a four-chambered heart and feathers; Y has a three-chambered heart and dry scales; Z has a two-chambered heart and gills. (i) Name the classes. [3] (ii) Which is warm-blooded? [1]

    Hint

    Use the clues.

    Answer

    (i) X: Aves; Y: Reptilia; Z: Pisces. (ii) X.

  10. Q10 · 4 marks · Case-basedHOTS / competency

    Case. A museum places a crocodile in the same class as a lizard and a whale with a rat. (i) Justify both placements. [3] (ii) Which of the four is cold-blooded? [1]

    Hint

    Reptile and mammal.

    Answer

    (i) The crocodile has dry scales and lays shelled eggs like a lizard; the whale has hair and mammary glands like a rat. (ii) Crocodile and lizard.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

  1. 1.Class with feathers?Show answer

    Aves.

  2. 2.Heart of a frog?Show answer

    Three-chambered.

  3. 3.Cold-blooded animals?Show answer

    Fishes, amphibians and reptiles.

  4. 4.Class of the whale?Show answer

    Mammalia.

  5. 5.Breathing organ of a tadpole?Show answer

    Gills.

Chordates: Fishes, Amphibians, Reptiles, Birds and Mammals: frequently asked questions

Is a crocodile an amphibian?

No, it is a reptile.

What is viviparous?

Giving birth to young ones.

Do birds have teeth?

No, they have a beak.