What is the difference between vertebrates and invertebrates?

Run your finger down the middle of your back. You can feel a row of bumps. They are part of your backbone, also called the spine, a chain of small bones that protects the nerves inside. Animals with a backbone are called vertebrates. Animals without one are invertebrates.

There are five main groups of vertebrates:

• Mammals, like dogs and whales (see mammals).
• Birds, like owls and penguins.
• Reptiles, like snakes and turtles.
• Amphibians, like frogs and newts.
• Fish, like salmon and sharks.

Vertebrates have a skeleton inside the body with a skull to protect the brain. Many have a hard skeleton of bone, while sharks have one made of tough, bendy cartilage. See the skeleton.

Invertebrates are a much bigger crowd. About 97 percent of animal species have no backbone. They include insects, spiders, snails, slugs, worms, crabs, starfish, jellyfish and octopuses. Some, such as insects and crabs, have a hard shell outside the body, called an exoskeleton. Others, like jellyfish and worms, are soft. Snails and clams carry a shell that is not part of a skeleton.

The largest invertebrates can be big: the giant squid can be over ten metres long. Still, most invertebrates are small. Without invertebrates, our world would not work, because they pollinate flowers, break down dead plants and feed other animals. Read more about insects to see one huge invertebrate group.

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