They are animals without a backbone. They have no internal skeleton and some have an exoskeleton a hard outer cover, like a crab or beetle).
Some live in shells like snails and clams and some are divided into segments like a worm.
There are thought to be about 5 million species of invertebrates around the world, which is about 95% of all animal life on Earth. They are found in the sea, on land, in the air and even in your body.
There are six separate groups, they are molluscs, echinodermis, annelids, cnidarians, arthropodis and sponges.
Without invertebrates the planet would not survive. Krill is a type of crustacean and it forms the basis of the food chain in polar seas.
Insects such as ants and beetles and their larvae help clean up the planet. While other insects such as bees are essential for pollination.