Nautiloids
Nautiloids are the only cephalopods with an external shell that are still alive today.
The living animal, Nautilus, is housed in a coiled shell, exposing only its head and tentacles to the outside world. Much of the shell is divided into chambers that are filled with gas. By adjusting the levels of gas the animal may live in the depths of the ocean and move to shallow water at night time to feed.
On the right, shell of recent nautiloid cut in half to show inner chambers.
Nautiloids first appeared about 500 million years ago. Then, there were many different species and they lived in the seas throughout the world.
Today, the few surviving species are found in seas around Australia and the Philippines.
They are often referred to as living fossils, as they have changed very little over millions of years.
On the right, a fossil nautiloid cut in half to show its inner chambers.
