A Blue View: Chambered Nautilus

At a glance, the chambered nautilus doesn’t appear to be anything special, but its simple design has remarkable staying power.

Published December 29, 2015

Chambered nautilus

This living fossil has roamed the ocean for millions of years and not much about its appearance has changed. A set of simple eyes sense light, and a group of about 90 tentacles extends from an opening at the base of its brown and white shell. Those tendrils are used primarily to sense and gather food. A sharp beak helps tear the food apart.

When faced with a predator, the nautilus pulls its body into its shell, sealing itself away from harm within its self-made armor. And it’s inside that shell that the real magic happens.

nautilus-shell-cross-section

Cracking open a chambered nautilus’ shell reveals a series of chambers arranged in a perfect logarithmic spiral—a spiral where the shape remains consistent even as its size increases. In the golden ratio, for example, at every quarter turn a spiral gets wider by a factor of phi, an irrational number with a value of approximately 1.618.

That same expanding spiral pattern can be seen throughout nature, from the winding of the Milky Way galaxy to the spiraling leaves and flowers of certain plants, like this romanesco broccoli:

romanesco-broccoli

As a nautilus grows, it continues to add new chambers to its shell. While a newly hatched nautilus has only four chambers, its shell can have upward of 30 as a mature adult.

The nautilus’ body resides in the largest chamber. With the others, the animal can control its buoyancy by modifying the ratio of liquid to gas in each. The nautilus is capable of diving thousands of feet during the day to avoid predators and returning to shallower waters at night to feed.

Episode Transcript

"This is the ship of pearl, which poets feign, sails the unshadowed main / and its dim dreaming life was wont to dwell /as the frail tenant of its growing shell."

Oliver Wendell Holmes described this remarkable creature in his 1858 poem “The Chambered Nautilus.” Holmes was a doctor, essayist, Harvard professor and Supreme Court justice.

However, the brilliant Holmes got the chambered nautilus wrong. It is not "a frail tenant." Not at all. Far from it.

The chambered nautilus is a robust survivor. A "living fossil." It has been around, relatively unchanged, for hundreds of millions of years. Two hundred and sixty-five million years before the dawn of the dinosaurs, the chambered nautilus was jet-propelling itself on the hunt for food with its long slim tentacles.

Those tentacles—of which it can have up to 90—are a giveaway to its ancestry. The nautilus is a cephalopod mollusk, a relative of octopus, squid, oyster and clam.

Yet, unlike its cousin, the famous giant Pacific octopus, the chambered nautilus has small eyes, blurry eyesight and sucker-less tentacles. It cannot open jars.

However, what it lacks in showmanship, it makes up for in beauty and longevity. It can live up to 16 years, while the giant Pacific octopus lives only three to five. At more than an inch in length, its eggs are among the largest of any invertebrate. Those eggs also have an extremely long incubation period: from six months to a year.

Nautilus are scavengers. They hunt by using their tentacles as chemical sensors—in effect smelling the deep reefs of the tropical Indo-Pacific carrion, dead and decaying crabs and fish, and occasionally other nautilus.

Now, about that shell—it's the only cephalopod to have one, and it is remarkable. Mathematical. A cross-section of the nautilus shell reveals that its chambers are arranged in a perfect logarithmic spiral.

Through a geometric principle called the golden ratio, these spirals are found frequently in nature. In sunflowers, for example. In hurricanes. In galaxies. And in the elegant lustrous mother-of-pearl whorl of a nautilus shell.

But that shell isn't just for show. It's functional. It provides shelter, defense, and it is a nifty swim aid.

The chambered nautilus can change its buoyancy in the water by adjusting the ratio of gas to saline solution in the chambers of its shell, much like a submarine uses its ballast tanks. In fact, the first nuclear powered submarine, launched in 1954, was named USS Nautilus.

The chambered nautilus can dive very deep, migrating 2,000 feet to cold, deep waters during the day to avoid predators like turtles, octopus and sharks, and then rising at night to feed in shallower, warmer waters.

We might love the nautilus's shell too much. In 2011, the New York Times called the harvest of their shells for jewelry and ornaments a "horrendous slaughter.” Sadly, nautiluses are heavily fished, and face possible extinction in the places where competition for the shell trade is fiercest, like the Philippines.

After surviving mass extinctions over millions of years, they are now at risk because we humans see a pretty shell, not the beauty of a survivor that’s stood the test of time.

To learn more about the nautilus and its shell’s golden ratio, please visit aqua.org/ablueview.

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