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Classification of Animals and Their Independence

Classification of animals is important to identify and know more about the animals. Animals are broadly categorised as vertebrates and invertebrates. In this concept, the students will understand some of the characteristics of animals and their interdependence.

After reading the concept, students will be able to:

  • Differentiate between worms and insects.
  • Know how many legs do insects have.
  • Explain the insect mouthparts and insect antenna.
  • Recall the names of worms such as earthworm, roundworm, etc.
  • Enlist the examples of fish such as Rohu fish, Catla fish, etc.
  • Categorise the animals on the basis of total number of heart chambers in them.
  • Describe the characteristics of warm-blooded and cold-blooded animals.
  • Answer how amphibians are different from mammals.
  • Discuss about parasitic nutrition.

Each concept is explained to class 4 students using descriptions, illustrations, and concept maps. After you go through a concept, assess your learning by solving the two printable worksheets given at the end of the page.

Download the worksheets and check your answers with the worksheet solutions for the concept Classification of Animals and their Interdependence provided in PDF format.

Animals can be broadly classified into two groups—

Identification of Animals:

We see different animals around us, and each of them possesses a set of unique features. Let us look at the identifying characteristics of some common animals.

1. Worms:

  • Worms are a group of invertebrates with soft and elongated bodies.
  • Worms have differently shaped bodies, such as tube-like, cylindrical, flattened or leaf-like.
  • Worms do not have limbs instead, they have bristle-like structures to grip surfaces.
  • Worms are found in both terrestrial and aquatic habitats.
  • Most worms depend on other animals for their nutrition.

Examples: Earthworm, roundworm, ribbon worm.

2. Insects:

  • Insects have segmented bodies with outer hard body covers.
  • Insects may have six to eight legs, and the legs are jointed.
  • The body of an insect can be divided into three parts—head, thorax and abdomen.
  • Mouthparts of the insects are present on the head.
  • Insects have a pair of antennae attached to the frontal part of the head. It is a sense organ used by the insect to assess its surroundings.

Examples: Mosquito, cockroach, ant.

3. Fish:

Fish are aquatic vertebrates living in both freshwater and saline water.Fish have gills to breathe inside the water.The body of fish is usually covered with scales.A fish has a streamlined body that helps swim swiftly in water.A fish has different fins that help in locomotion and help maintain balance inside water.Fins also help in changing directions inside water.

Examples: Rohu, Catla, salmon, pufferfish, tuna etc.

4. Amphibians:

  • Amphibians are vertebrates that can live on land and in water in their adult stage.
  • Amphibians have moist skin to breathe inside water. However, they also possess lungs to breathe when they are on land.
  • Some amphibians have tails.
  • Amphibians mostly lay eggs on the water surface.
  • They may either have limbs or not.

Examples: Frogs, toads, newts, salamanders etc.

5. Reptiles:

  • Reptiles are air-breathing, cold-blooded vertebrates.
  • They have lungs for breathing.
  • The bodies of the reptiles are covered with dry scales that help in moisture retention.
  • Reptiles either have a three or four-chambered heart.
  • Some reptiles have prominent legs, but some do not, such as snakes.
  • Reptiles are found in both land and water.

Examples: Turtle, alligator, crocodile, snakes.

6. Birds:

  • Birds are vertebrates, and they possess feathers, wings and beaks.
  • They are warm-blooded and have a four-chambered heart.
  • The body of a bird is covered with feathers.
  • Their forelimbs are modified into wings.
  • Birds lay hard-shelled eggs.
  • The body of a bird is divisible into three parts—head, neck and trunk.
  • Birds use their beaks to eat.
  • Birds have air sacs in their bodies, and their bones are light. As a result, they can easily fly.

Examples: Crow, pigeon, sparrow, duck.

7. Mammals:

  • Mammals are vertebrates having mammary glands.
  • The young ones are nourished with milk from the mammary glands of the mother.
  • The mammalian heart has four chambers.
  • Mammals have external ears, and their bodies are covered with hair.
  • Mammals do not lay eggs; rather, they give birth to young ones.
  • A typical mammalian body is divisible into four parts—head, neck, trunk and tail. However, some mammals do not have a tail.

Examples: Whale, rat, cat, bat, tiger, human, elephant.

Interdependence Among Animals:


  • It is a biological interaction where animals hunt and kill other animals to satisfy their hunger.
  • The animal that hunts is called the predator, while the animal that is hunted is called the prey.
  • Carnivorous or flesh-eating animals usually feed on herbivorous or plant-eating animals.

Examples: A tiger hunting a deer, an eagle killing rats and snakes.


  • Parasitism is the relationship between two species of plants or animals, in which one gets benefitted at the expense of the other.
  • The one who gets benefitted is called the parasite.
  • The organism which provides the benefit is called the host.
  • The parasite derives nutrition from the host.
  • In such a relation, the host gets harmed by the parasite’s activity.
  • Parasites can either live on the body surface of the host or inhabit inside the host’s body.

Examples: Lice reside on the scalp of humans and suck blood for nutrition and, in turn, damage the scalp, fleas extract their food by living on the body surfaces of cats and dogs.


  • In this kind of interaction, both the organisms involved get mutually benefited.

Examples: Mutualism is exhibited by the oxpecker and rhinoceros. The oxpecker eats fleas, ticks and other insects that reside on the rhinoceros’ skin, and in return, the rhinoceros gets pest control service from the oxpecker. So, both are benefited from this relationship.


 New Words:

Mouthparts: A structure near an insect’s mouth specially adapted for gathering and eating food.

Streamlined: A body shape that tapers at both ends.

Locomotion: The ability to move from one place to another.

Warm-Blooded Animals: Animals that are able to maintain their body temperature irrespective of the temperature of the environment.

Cold-Blooded Animals: Animals that are not capable of controlling their body’s temperature according to the temperature of the surrounding.


Did You Know?

  • Whales and dolphins are aquatic mammals because both are air-breathing animals, have mammary glands and give birth to young ones.
  • Kangaroos are mammals, but have brood pouches where they carry their babies until they are fully developed.
  • Platypus and spiny anteaters are mammals that lay eggs.
  • Dinosaurs were also reptiles, but they became extinct about 65 million years ago.

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