There are five classes of animals which are alike in one important way. Every animal has a skeleton. A skeleton is made up of bones that help to support the animal's body. These animals have a backbone that is made up of many small bones. The backbone helps the animal bend and move.

• Animals with backbones can be divided into five classes:

1 mammals

2 amphibians

3 birds

4 reptiles

5 fish

There are small animals which do not have backbones. Some of them live in water. They can be divided into the following classes:

Animals with spiny skins:

They have rough skin with sharp needle-like spines. Their bodies are divided into five parts. Examples include starfish and sea urchins.

Animals with shells:

Most of these animals live on land. They have soft bodies. Most of them have a hard shell outside their bodies. Examples include snails and oysters.

Worms:

All worms have soft bodies. They do not have legs. They live on land and in water. Examples include earthworms, roundworms and tapeworms.

These animals have many legs with many joints. Their bodies are divided into many parts and they have a hard outer skin.

Spider • leg

Butterfly • wing & leg

Crab • hard skin

The body of an insect has three parts: the head, the thorax, and the abdomen.
It has two compound eyes and two antennae on its head.
It has mouth parts that can chew or suck food.

Grasshopper External Anatomy

Fish live in water. They are of many shapes, colours, and sizes. All fish have a backbone. They breathe in water through their gills. Most fish have scales on their skin. They swim in the water with their fins.

An amphibian is an animal that spends part of its life in water and part of its life on land. Young amphibians live in water and breathe through their gills like fish. As they grow older, they breathe through their lungs and live on land.

Frog (Adult • Lungs)

Salamander • Land