More than a million and a half species of animals have been identified and there are many millions more yet to be discovered. Animals are living organisms found in nearly all of the earth’s habitats including the depths of the oceans, the freezing arctic and even inside other animals and plants. The animal kingdom is divided into animals without backbones (invertebrates), such as snails and lobsters and animals with backbones (Vertebrates), such as frogs and monkeys. Invertebrates make up 97 per cent of all animal species.

Black Leopard:

The leopard is a mammal. Its well–defined head is equipped with sense organs, including eyes, nose, tongue and whiskers. Sharp teeth in the mouth allow the leopard to kill prey and tear off flesh. Muscular legs enable it to walk, run and pounce.

What Is an Animal?

Animals are made up of many cells. Most move actively and those that are fixed in one place or sedentary move their body parts. Animals live by taking food into their bodies. They have sensors and nervous systems that enable them to detect what is happening around them and respond appropriately.

Animal Classification:

Animals are classified into groups according to their similarities and whether they have common ancestors. There are 35 major groups called phyla (Singular Phylum). Each phylum is divided into sub–groups. The smallest of these is the species which contains animals of just one type.


The simplest animals are sponges (Phylum Purifiers). There are above 5,000 species, most of which live in the sea attached to rocks and other objects. Water is drawn in through holes or pores in the sponge’s body wall and bits of food are filtered out and eaten by the sponge’s cells.


There are more than 9,000 species of cnidarians (Phylum Cnidaraia). Most of which are found in the sea. They include jellyfish, sea anemones, hydras and corals. Cnidarians catch food using tentacles armed with stinging threads called nematocysts.


These worms (Phylum Platyheminthes) have a flattened body with one opening with the mouth on the underside. There are about 18,500 species including those, such as tapeworms, that are parasites of humans and other animals.


Animals in the phylum annelids include earth worms, marine bristle worms such as rag worms and leeches. There are about 12,000 species. Each of which has a body made up of segments with mouth at one end and an anus at the other.


All echinoderms (Phylum Echinoderm) live in the sea. The 6,500 or so species include sea urchins and starfish. Most have five parts radiating from central points, hard plates under the skin and many tube–feet.


Roundworms or nematodes (phylum nematodes) have a thin, cylindrical body that is pointed at both ends. Free-living nematodes are found in many habitats and occur in very large numbers in soil. Many nematodes are parasites of plants and animals.


Molluscs (Phylum Mollusca) form a highly diverse group of about 50,000 species. These include snails. These include snails and slugs, mussels and clams and squids and octopuses. They are soft bodied animals that may be protected by a shell. Most live in water, but some, such as snails, are found on land.


With at least one million known species, arthropods (Phylum Arthropod) are the largest group of animals. They include insects, crustaceans such as crabs, arachnids (such as spiders) and centipedes.


There are about 48,000 species of chordate (Phylum Chordata). Most are vertebrates, such as fish, amphibians, reptiles, birds and mammals. Vertebrates are the most advanced animals.

Animal’s Skeletons:

The skeleton is a supportive framework that maintains the shape of an animal and enables it to move. Most skeletons are hard structures, either inside or outside the animal’s body, to which muscles are attached. The skeleton may also protect internal organs and in the case of an insect’s external skeleton prevent the animal from drying out.

Internal Skeletons:

A skeleton found inside the body is called
Endoskeletons. Most vertebrates have a skeleton made of cartilage and bone. Joints between the bones allow the animal to move. The endoskeleton grows with the rest of the body.

External Skeletons:

A hard outer skeleton that covers all or part of the body is called an
Exoskeleton. An insect’s outer cuticle and a snail’s shell are examples of exoskeleton. An insect’s exoskeleton does not grow and mush be shed or mounted periodically to allow the animal to grow.

Hydrostatic Skeleton:

The Hydrostatic Skeleton is an internal skeleton found in soft-bodied animals such as earthworms. It consists of a fluid-filled core surrounded by muscles and maintains the shape of the worm.

Animals Movement:

The ability to move is characteristic of animals, which move to find food, escape from predators, and find a mate. The way in which an animal moves depends on its complexity, lifestyle, and where it lives. The wide range of movement includes swimming through water, walking and creeping on land, and flying or gliding in air.

Moving In Water:

Many aquatic animals are adapted for movement in water by having streamlined bodies. Most fish move by pushing their tail fin from side to side. This pushes the water backward and sideways and propels the fish forward. Whales move in a similar way except that the tail moves up and down.

Movement in Air:

Insects, birds and bats are capable of powered fight using wings. Birds have lightweight, streamlined bodies. They use energy to flag their wings which push them forward. As air passes over the wings ii creates the life that keeps the bird in the air.

Movement on Land:

Animals move on land in a variety of ways. Many have limbs that raise the body off the ground, support it and enable the animal to walk, run or hop. The animals move forward by pushing the ends of their legs or feet backward against the ground.

Animal Senses:

The main senses are vision, hearing, tastes, smell ands touch. Animals use their sense to find out what is going on around them. A stimulus from outside, such as a sound, is detected by a sense organ, such as the ear. Nerve impulses from sense organs are interpreted by the animal’s brain which decides how to respond.


All animals feed by taking in food. They use a range of feeding strategies and can be grouped accordingly. Some animals kill and eat. Others graze to browse on plants. Others filter food particles from water. After fee ding or ingestion food is digested so that it can be used by the body.

Filter Feeders:

These are animal that feed by sieving food particles from water that flows into their body. Many are sedentary and draw in a current of water. Some whales are filter feeders that eat small animals called krill.


Animals that feed solely on plants are called herbivores. Many use specialized mouthparts, such as grinding teeth, to break up tough plant tissues. Plant material is not a rich food source and most herbivores eat a lot to obtain the necessary nutrients.


These types of feeders are adapted to detect prey animals to catch and kill them and to cut them up to eat them. They include cats, eagles and some insects. Dragonfly larvae live in water and they can catch small fish to eat.


Eyes contain sensors that are sensitive to light. When stimulated they send nerve impulses to the brain which enable it to build up a picture. Insects have compound eyes made up of many separate units or immaterial.


These are found on the head of arthropods such as insects. They are used to detect odors and may detect chemicals called pheromones released by insects to communicate with each other. Antennae also detect vibrations and movements in the air or in water.


Some animals can detect sounds with ears. The ear converts sound into nerve impulses that can be interpreted by the animal’s brain. Animals use sounds to communicate with each other and to detect approaching predators or prey.

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