Corals are made up of small invertebrate animals, known as zooids, that look like tiny sea anemones. They feed on small food particles they find in the water around them.
Together, many zooids form colonies, many colonies form reefs. Coral reefs can be massive structures, stretching hundreds of miles. The Great Barrier Reef in northern Australia can be seen from space.
The oldest coral fossils are over 500 million years old. The earliest forms were different from those we see today and they died out 225 million years ago. Modern corals are still common in tropical oceans.