Half a billion years before the first submarine left harbor, the ancestors of our modern nautiluses were already beginning to master the art of buoyancy control. How do these creatures work? Read on.

1. THERE ARE SIX RECOGNIZED SPECIES.

The chambered nautilus (Nautilus pompilius) is hands-down the most famous of these cephalopods. The orange-banded creature shares its genus with three other species, known as the Palau, bellybutton, and white-patch nautiluses (with a potential fourth, Nautilus repertus, though most scientists believe it's actually a large chambered nautilus). Meanwhile, the lesser-known Allonautilus genus contains two rarely-seen species—one of which we’ll discuss later on.

With shells that measure up to 10.6 inches in diameter, chambered nautiluses are the largest of the six, and bellybuttons—whose shells max out at 6.3 inches in diameter—as the smallest. Range-wise, these animals are all restricted east-west within the waters between Samoa and the Philippines, and north-south between Japan and Australia.

2. UNLIKE ITS FELLOW CEPHALOPOD THE OCTOPUS, THE NAUTILUS HAS A POOR MEMORY.

From the meaning of certain symbols to how to open child-proof lids, an octopus can remember a lot—and retain that knowledge long-term. Nautiluses, in contrast, aren’t regarded as being very bright; in fact, until recently, it was believed that they weren’t capable of forming any memories whatsoever.

Marine biologists Robyn Cook and Jennifer Basil of Brooklyn College and the City University of New York, respectively, wondered if this assumption was true—so in 2008, the pair trained captive nautiluses to associate a flashing blue light with food. After a while, the animals reacted strongly whenever this signal came on, spreading their arms in eager anticipation. However, they stopped doing so the following day. Why? Presumably, the invertebrates had managed to forget everything they’d learned within a 24-hour period.

3. THEY’RE RELATIVELY LONG-LIVED.

Squids and octopuses don't usually live long lives—in fact, most die after just two to three years. By comparison, nautiluses look like Methuselah: 17-year-old specimens have been caught, and biologists theorize that some can surpass 20 years old.

4. THEY USE AN AMAZING BUOYANCY-CONTROL MECHANISM.

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Nautilus shells have a series of chambers connected by the siphuncle—a tube made of tissue. A newborn nautilus starts life with four chambers, adding more and more as it grows (adults have 30 on average). The chambers contain a mixture of gas and seawater, and the siphuncle regulates how much of each is present within the chambers at any given time.

If a nautilus wants to descend, the siphuncle makes that happen by pumping sodium and chlorine ions into the chambers. Extra water then enters these compartments thanks to osmosis, making the animal less buoyant, and the nautilus sinks. To reverse this process and travel upward, the siphuncle simply removes ions from the chambers, and water consequently flows into the mantle cavity. As it leaves, gas bubbles start to diffuse, which lightens the shell.

5. NAUTILUSES RELY ON JET PROPULSION.

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The mantle cavity, a funnel below the eyes and present in all cephalopods, is connected to a muscular siphon. Nautiluses move forward and backward by aiming this tube and rapidly expelling water through it.

6. NAUTILUS SHELLS IMPLODE AT A CERTAIN DEPTH. 

Nautiluses are usually found between 500 and 1000 feet below the surface, and within that range, their shells hold up quite well. But going too deep can be a fatal mistake. For chambered nautiluses, 2575 feet appears to be the limit. During one 1980 experiment [PDF], a captive specimen was subjected to the amount of pressure that it would naturally encounter at this depth. Moments later, the shell imploded, killing the creature instantly.

7. CHAMBERED NAUTILUSES HAVE UP TO 90 ARMS.

These short, clustered limbs help ensnare the fish, crabs, and carrion upon which the cephalopods dine. Speaking of mealtime, hungry nautiluses use scent to track down food because they can’t see very well (their eyes lack lenses) so their eyes are more akin to pinhole cameras, which, according to the book Animal Eyes, forces them to choose between “unusably dim or unusably blurred.”

8. NAUTILUSES USE ADHESIVES TO GRAB THINGS.

Octopuses and squids employ suckers and hooks, which nautiluses lack. Instead, their arms are coated with a sticky substance that helps ensnare prey. Tiny hairs called cilia also help form viscous pads near the appendages’ tips.

9. SOME SPECIES PROTECT THEMSELVES WITH SLIME.

“It’s really a very cool way not to get eaten,” earth scientist Peter Ward told Live Science. Last August, the University of Washington professor became the first person in 31 years to spot a rare nautilus species. Allonautilus scrobiculatus is easily recognized due to its odd defense mechanism: Thick, slimy fuzz coats the animal’s shell, making it too slippery for many fish and other predators to bite into.

10. CHAMBERED NAUTILUS EGGS ARE THE LARGEST OF ANY KNOWN CEPHALOPOD.

Most cephalopod eggs are incredibly small: Those laid by the 50-pound giant Pacific octopus, for example, are about as big as a grain of rice. Around an inch long, chambered nautilus eggs dwarf the competition. Using her tentacles, a female will (presumably) affix the eggs to a hard surface, where they’ll hatch between nine and 12 months later.