Sea urchin

Where does the sea urchin live?

Home: on rocks and in rock pools of the Mediterranean and eastern Atlantic.

In the wild it lives in these countries: Spain, France, Italy, Portugal, Greece, Morocco, Ireland, the United Kingdom.

The short profile

Fully grown: shell 5 to 7 cm across, spines about 3 cm. It weighs about 0.08 kilograms. On the menu: plants.

The story behind it

The round shell of a sea urchin is called a test and is built from plates that fit together like tiles. Every spine rests on a little ball joint, so it can tip and push, while between the spines the tube feet reach out and grip. Spines and feet together carry the urchin over the rock, a few centimetres a minute. Underneath hides the oddest part: five hard teeth held in a frame of muscles and chalky rods that people call Aristotle's lantern. Aristotle described this chewing gear more than 2300 years ago, though some researchers now think he was comparing the whole animal to a lamp rather than just the mouth. The teeth scrape algae off stone all day and keep growing, because scraping wears them down.

Find it on the globe

Sea urchin is there as a tiny animated figure that breathes and looks around. From far away the planet is only a blue ball; detail arrives as you zoom in, and this one appears once you are close enough. Open it on the globe.

It sits at its real coordinates, not near them — the same numbers listed in the facts above. Switch off the layer for this kind of place and it disappears again; the buttons for that are down the right-hand edge.