What animal builds itself an apartment building?

If you’ve ever seen pictures of a coral reef, you might have seen something that looks like a colourful underwater forest. Some corals are tall and branching, some are small and round, but each coral isn’t just one living thing – it’s a home to thousands of them!

Corals are related to anemones and jellyfish, and their bodies look very similar: a clear bag of liquid with a mouth surrounded by tentacles. Each one of those tentacles is full of tiny stingers, so that when prey swim past, they are grabbed by the tentacles and stung until they can’t fight back.

But unlike anemones and jellyfish, corals stay in one place and build themselves a house!

Each individual animal in coral is called a polyp. To make coral, several polyps get together to make a hard shell. When they’re finished, each coral is home to many polyps – just like an apartment building.

When the coral want to eat, they stick their tentacles out of holes in the shell, but if danger threatens, they can yank their tentacles back inside where it’s safe!

Growing a reef takes a long time – coral grow anywhere from 0.2 to 8 mm each year. The Great Barrier Reef is 2600 km long – that means it must have been growing for at least 325 million years!