9 Fascinating Facts About the Nautilus

Learn About These Living Fossils

01
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Introduction to Nautiluses

Chambered nautilus swimming
Stephen Frink/Image Source/Getty Images

Year after year beheld the silent toil
  That spread his lustrous coil;
  Still, as the spiral grew,
He left the past year's dwelling for the new,
  Stole with soft step its shining archway through,    
   Built up its idle door,           
Stretched in his last-found home, and knew the old no more.

- Excerpt from The Chambered Nautilus, by Oliver Wendell Holmes, Sr.

Nautiluses are living fossils that have been the subject of poetry, artwork, math and jewelry. The have even inspired submarines and exercise equipment. These animals have been around for about 500 million years  - even before the dinosaurs.

 

02
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Nautiluses have many tentacles

Cross-section model of chambered nautilus
Cross-section model of chambered nautilus. Geoff Brightling/Dorling Kindersley/Getty Images

Nautiluses have many more tentacles than their squid, octopus and cuttlefish relatives. They have about 90 tentacles, but they do not have suckers. Squid and cuttlefish have two and octopus have none.

The shell may be up to 8-10 inches across. It is white on the underside and has brown stripes on its upper side. This coloration helps the nautilus blend into its surroundings. 

How does a nautilus move?

A nautilus moves by Through jet propulsion. Water enters the mantle cavity and  is forced out the siphon to propel the nautilus backward, forward or sideways.

03
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Nautiluses are related to octopus, squid and cuttlefish

Nautilus Close Up
Michael Aw/DigitalVision/Getty Images

 

Nautiluses are cephalopods, mollusks related to octopus, cuttlefish and squid. Of the cephalopods, nautiluses are the only animal to have a visible shell. And what a shell it is!  Their shell is so beautiful that harvesting has caused a decline in some populations. 

These several species are in the Nautilidae family, which contains four species in the genus Nautilus and two species in the genus Allonautilus. The shells of these animals may grow from 6 inches (e.g., bellybutton nautilus) to 10 inches (e.g., chambered or emperor nautilus) in diameter.​

Allonautilus was recently re-discovered in the South Pacific after 30 years. These animals have a distinctive, fuzzy-looking shell. 

04
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Nautiluses are buoyancy experts

Close-Up Of Nautilus In Sea
Jose Luis Tirado / EyeEm / Getty Images

The shell of an adult nautilus contains over 30 chambers. These chambers form as the nautilus grows, into a shape called a logarithmic spiral.  

The chambers are ballast tanks that help the nautilus maintain buoyancy. The nautilus's soft body is located in the largest, outermost chamber. The other chambers are filled with gas. A duct called the siphuncle connects the chambers. When needed, the nautilus can flood the chambers with water to make itself sink. This water enters the mantle cavity and is expelled through a siphon.

An Inspiring Design

These chambers inspired the design of Jules Verne's submarine Nautilus in 20,000 Leagues Under the Sea, and the logarithmic spiral cam in Nautilus exercise machines. The first nuclear submarine was called the U.S.S. Nautilus.

Withdrawing for Protection

Not only is the shell beautiful, it provides protection. The nautilus can protect itself by withdrawing into the shell and sealing it closed with a fleshy trapdoor called a hood.

 

05
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Nautiluses can't dive too deeply, or their shells will implode

Chambered Nautilus (Nautilus belauensis), Micronesia, Palau
Reinhard Dirscher/WaterFrame/Getty Images

Nautilus live in tropical and warm temperate waters near reefs in the Indo-Pacific region. During the day, they live primarily in waters up to about 2,000 feet. Much past that depth, their shells will implode.

At night, nautiluses feed closer to the ocean surface.

06
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Nautiluses are active predators

Sea Shells in the Mentawai Islands
John Seaton Callahan / Getty Images

Nautiluses are active predators and most often feed at the surface at night time. They use their tentacles to grip prey, which they rip with their beak before passing it to the radula. Their prey includes crustaceans, fish, dead organisms and even other nautiluses. It is thought that they find their prey by smell. Although nautiluses have large eyes, their vision is poor. 

07
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Nautiluses reproduce slowly

Two nautiluses
Richard Merritt FRPS/Moment/Getty Images

With a lifespan of 15-20 years, nautiluses are the longest-living cephalopods. They also may reproduce multiple times (other cephalopods may die after reproducing just once).  

Nautiluses may take 10-15 years to become sexually mature. They mate sexually. The male transfers his sperm packet to the female using a modified tentacle called a spadix. The female produces about a dozen eggs and lays them one at a time, a process that may last throughout the year. It can take up to a year for the eggs to hatch. 

 

08
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Nautiluses were around before the dinosaurs

High Angle View Of Nautilus Fossils Table
Douglas Vigon / EyeEm / Getty Images

Long before dinosaurs roamed the Earth, giant cephalopods swam in the sea.  The nautilus is the oldest cephalopod ancestor. It hasn't changed much over the last 500 million years, hence the name living fossil. 

At first, prehistoric nautiloids had straight shells, but these evolved into a coiled shape. Prehistoric nautiluses had shells up to 10 feet in size. They dominated the seas, as fish hadn't yet evolved to compete with them for prey.  The nautilus's main prey was likely a type of arthropod called the trilobite.

 

09
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Nautiluses may become extinct due to overfishing

Polished chambered nautilus shell
Polished chambered nautilus shell. Science Photo Library/Getty Images

Threats to nautiluses include over-harvesting, habitat loss and climate change.  One climate change-related issue is ocean acidification. This will affect the nautilus's ability to build its calcium carbonate-based shell.

Overharvesting

Nautilus populations in some areas (such as the Philippines) are declining due to overfishing.  They are caught in baited traps and used for the shell itself and the mother-of-pearl (nacre) inside the shell. They are also caught for their meat and for use in aquariums. According to the U.S. Fish and Wildlife Service, more than half a million nautiluses were imported into the U.S. in 2005-2008. 

Nautilus are especially vulnerable to overfishing due to their slow development and reproduction rates. Nautilus populations also seem to be isolated, with little gene flow between populations and less ability to recover from a loss.

Despite concerns about population declines, nautiluses are not yet considered endangered. The IUCN has not yet reviewed nautilus for inclusion on the Red List due to lack of data.  Restricting trade under the Convention on International Trade in Endangered Species (CITES) would better protect populations, but that has not yet been formally proposed. 

10
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You can help save the nautilus

Diver watching Palau nautilus
Diver watching Palau nautilus. Westend61/Westend61/Getty Images

If you would like to help nautiluses, you can support nautilus research and avoid purchasing products made of nautilus shell.  These include the shells themselves, and "pearls" and other jewelry made from the nacre from the nautilus's shell. 

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