The nautilus is a living fossil, unchanged for hundreds of millions of years. Although divers see them infrequently, they are most common in the tropical western Pacific.

The nautilus is a living fossil, unchanged for over 500 million years. Fossil hunters frequently uncover remnants of these cephalopods in the Sahara and Gobi Deserts, individuals that died during the Cretaceous Period. Along with the elusive coelacanth and horseshoe crab, the nautilus is one of the last creatures on the planet to remain unchanged for millennia.

Related to octopus, cuttlefish and squid, nautiluses are the only cephalopods to have visible shells. Their vibrant covering, in fact, is their most distinct attribute. With six species surviving from a high of more than 10,000 species, the chambered nautilus is the most common in the modern era, inhabiting the tropical western Pacific from the Great Barrier Reef to the Andaman Sea. This is also the largest species, reaching a size of up to 10 inches (25 cm) in exceptional cases.

Characteristics of the nautilus

The chambered nautilus’ shell allows the species to excel in terms of survival. Its countershading means that its lighter coloration on the bottom and darker shading work together to create camouflage against predators, which include sharks, turtles and triggerfish.

To feed, the nautilus ascends each evening from daytime depths that exceed 1,500 feet (450 m) to shallower reefs of around 300 feet (90 m) to feed on crabs, shrimp and smaller fish species. With over 90 sucker-less tentacles attached to their head, nautiluses use the grooves and ridges of their tentacles to grip prey before consuming food with their beak.

Flawless buoyancy is another notable nautilus characteristic, of vital importance since they free-float in the deep-water column. When nautiluses are newly hatched, their shells are divided into four compartments. Over the years, these compartments can divide into as many as 38, with the body contained in the largest and oldest compartment. Controlling the water and air throughout these compartments, a nautilus can easily maintain its buoyancy, whether it be negative, positive or neutral. They use jet propulsion to regulate their movement, much like squid, blowing water out of a flexible siphon beneath their tentacles. A nautilus can also completely retract its tentacles and body into its shell, closing off the opening with a leathery hood.

The lifespan and future of the nautilus

Reaching ages of 20 years old, a nautilus takes 5-6 years to reach sexual maturity and, with a combined gestation period of 9-12 months, they are often threatened by humans who wish to use their ornate orange and white shells for decoration and festive trinkets. Unfortunately, many countries still export the shells. Others, such as Indonesia, are setting the example, banning the exportation of the nautilus, and trying to preserve this magnificent prehistoric creature.

Have something to add to this post? Share it in the comments.
New stuff

Tulagi: the Perfect Choice for Rust and Reefs

Cross the famous watery graveyard of Iron Bottom Sound from Honiara, capital of the Solomon Islands, and you’ll find a hidden gem for lovers of wrecks and reefs: Tulagi.
by Deborah Dickson-Smith
dive limits

Training Fundamentals: Following Recommended Dive Limits

Each qualification has recommended dive limits for depth or activity. Why are the limits there? Why is it wise to follow them?
by Marcus Knight
diving fix

How to Get Your Diving Fix While on Lockdown

If, like us, you’re spending most of your time at home right now, there are still ways get your diving fix — and stay connected to the rest of the diving community.
by Yvonne Press
cleaning dive gear

Cleaning Dive Gear in Times of Covid-19

When it comes to cleaning dive gear, our biggest worry is usually removing saltwater. As the world tries to slow the spread of Covid 19, keeping gear clean has taken on a whole new meaning.
by Yvonne Press