It may not be as slinky or showyas its cephalopod cousins the octopus, cuttlefish and squid, but the chambered nautilus (Nautilus pompilious) has some very distinguished credentials of its own.

First, it's the oldest cephalopod. Really old. The nautilus dates back 150 million years, and has changed little over the ages. It's considered a living fossil.

Some of its bodily functions are pretty primitive, too. Its simple eyes can only sense dark and light, like a pinhole camera. Rather than rely on speed or camouflage for protection like its cousins, the nautilus has kept its shell.

When it really needs to hunker down it can even shut itself completely inside, covering the opening with a leathery hood formed by two specially folded tentacles.

As the nautilus grows it adds chambers to its shell - each one slightly larger than the last to accommodate its bigger body. It controls its buoyancy by moving fluids in and out of those chambers.

Like its cephalopod kin, the nautilus has tentacles. But unlike those kin, the nautilus has more than 90 - the most in its family - with which to touch and taste the world. They don't have suckers, however. Instead, grooves and ridges grip food and pass it to the nautilus's mouth, where a parrotlike beak rips the food apart - a function shared with other cephalopods.

Nautilus, Interrupted

Nautiluses also live longer - a lot longer - than their cousins; they may live for more than 20 years, as compared to about two years for most octopuses, cuttlefishes or squid.

These mysterious cephalopods are under increasing threats from fishermen seeking to cash in on the nautilus's unique shell, with its attractive shape and pearlescent chambered interior - which also just happens to form nature's finest example of a perfect logarithmic spiral.

Currently there are no national or international regulations to protect the nautilus, but it is said some biologists have begun the conversation.

You can see more than 30 living nautiluses in our Tentacles special exhibition - the most on exhibit anywhere. You won't find any shells in our gift shops, for good reason.

Learn more about the chambered nautilus in our animal guide or podcast.

Our thanks to National Geographic photographer Joel Sartore for the wonderful images of our animals that he created for his PhotoArk project.

This blog was orginally posted on the Monterey Bay Aquarium's Tumblr page.