Nautilus pompilius Shell

Nautilus pompilius, an externally shelled cephalopod, a type of mollusk. Cephalopods are found in all of the world's oceans, from the warm water of the tropics to the near-freezing water at the poles.

Cephalopods are an ancient group that appeared some time in the Late Cambrian, several million years before the first primitive fish began swimming in the ocean. Scientists believe that the ancestors of modern cephalopods such as octopus, squid and cuttlefish, diverged from the primitive externally shelled nautiloidea (nautilus) very early on, possibly in the Ordovician some 438 million years ago. Nautilus has been around for 500 million years and are considered living fossils. (Year of image: 2003)