No, animal classes are not like the classes people have at school!

An animal class is made up of animals that are all alike in important ways. Scientists have grouped animals into classes to make it easier to study them.

There are many different animal classes and every animal in the world belongs to one of them. The five most well known classes of vertebrates (animals with backbones) are mammals, birds, fish, reptiles, amphibians. They are all part of the phylum chordata -- I remember "chordata" by thinking of spinal chord.

There are also a lot of animals without backbones. These are called invertebrates and are part of the phylum arthropoda (arthropods). Two of the most commonly known classes in this phylum are arachnids (spiders) and insects.

People are mammals. So are dogs, cats, horses, duckbill platypuses, kangaroos, dolphins and whales. What do all these animals have in common, you ask?

The answer is – MILK! If an animal drinks milk when it is a baby and has hair on its body, it belongs to the mammal class.

Birds are animals that have feathers and that are born out of hard-shelled eggs.

Some people think that what makes an animal a bird is its wings. Bats have wings. Flies have wings. Bats and flies are not birds. So what makes an animal a bird?

The answer is feathers!

All birds have feathers and birds are the only animals that do. The feathers on a bird¡¯s wings and tail overlap. Because they overlap, the feathers catch and hold the air. This helps the bird to fly, steer itself and land.

Fish are vertebrates that live in water and have gills, scales and fins on their body. There are a lot of different fish and many of them look very odd indeed. There are blind fish, fish with noses like elphants, fish that shoot down passing bugs with a stream of water and even fish that crawl onto land and hop about!

Reptiles are a class of animal with scaly skin. They are cold blooded and are born on land.

Snakes, lizards, crocodiles, alligators and turtles all belong to the reptile class.

Amphibians are born in the water. When they are born, they breath with gills like a fish. But when they grow up, they develop lungs and can live on land.

Arthropods is a huge phylum of animals -- it includes eleven animal classes: Merostomata, Pycnogonida, Arachnida, Remipedia, Cephalocarida, Branchiopoda, Maxillopoda, Malacostraca, Chilopoda, Diplopoda, and Insecta.

Any animals that have more than four, jointed legs are arthropods. Insects, spiders and crustaceans all belong to this class of animals.