Nautilus

The nautilus is a shelled cephalopod that keeps to deep tropical waters. It glides while inside a coiled shell divided into chambers. It is slow-growing, long-lived, and has a body structure that has barely changed for hundreds of millions of years.

 Image showing Nautilus (source: Manuae)

Scientific classification

• Kingdom: Animalia
• Phylum: Mollusca
• Class: Cephalopoda
• Subclass: Nautiloidea
• Order: Nautilida
• Family: Nautilidae
• Genera: Nautilus, Allonautilus (six known living species)

Physical characteristics

• Nautiluses carry a coiled shell, usually pearly, sometimes ornate.
• Inside, chambers connect via a tube called a siphuncle; the animal lives in the outermost chamber and fills or drains inner ones with gas.
• They drift on jet propulsion, pushing water through a hyponome. They have many suckerless tentacles, up to ninety-four, used for sensing food and handling prey.

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Habitat and distribution

• Nautiluses live in deep tropical waters of the Indo-Pacific, usually at depths of a few hundred meters.
• At night they rise closer to the surface, but usually avoid water that is too warm

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Diet and feeding habits

• They are scavengers and opportunistic hunters.
• Nautiluses feed on crustacean molts, small crabs, fish, even carrion.
• Their sensitive tentacles detect scents, and the mouth’s beak breaks down prey

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Life cycle and reproduction

• Nautiluses grow slowly and live long, up to a couple of decades or more.
• The best-known species (N. pompilius) matures around 10 to 15 years and carries eggs for long periods before hatching.
• Their pace is unlike most cephalopods, which live short lives.

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Behavior and adaptations

• Nautiluses maintain buoyancy by adjusting gas levels in their shell chambers.
• At night, they move upward to feed, then return deeper during the day.
• Their striped shell patterns are unique to individuals, like a fingerprint.

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Ecological importance

• They link deep sea detritus and shallow food webs.
• Many ocean animals prey on them, and they slowly tease energy upward via scavenging.
• Their ancient, unchanged lineage gives insight into cephalopod evolution.

All known species or breeds

Here are a few living nautilus species, grouped by shell type and known traits:

1. Nautilus pompilius (chambered or pearly nautilus)
Typical shell size up to 25 cm, about 30 chambers. Found across the Indo-Pacific. Two subspecies: the widespread N. p. pompilius and the smaller N. p. suluensis in the Sulu Sea

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2. Nautilus macromphalus (bellybutton nautilus)
Known for having an exposed shell umbilicus that shows inner coils (~15 % of shell width). Lives near New Caledonia, Australia; shell up to 16 cm

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3. Nautilus belauensis (Palau nautilus)
Deep-water dweller off Palau. Moves from 150 m down to 300 m but can tolerate near 30 °C briefly. Scavenger active day and night

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4. Nautilus vanuatuensis
Described in 2023; has bright red shell stripes covering a large part of the shell. Found in Vanuatu, usually at 200–400 m but seen as shallow as 5 m

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5. Allonautilus scrobiculatus (“crusty nautilus”)
Rare and elusive, with a slimy shell layer. Sighted again in 2015 after decades. It migrates differently, vertically up reef faces at night—and its slippery shell maybe stops predators from grabbing it.

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Threats and conservation status

• Nautiluses are under pressure from shell trade.
•  N. pompilius declined nearly 80 % in the Philippines. That species is now listed as threatened under the U.S. Endangered Species Act, and all nautiluses are included in CITES Appendix II to regulate trade.
• Habitat damage and ocean acidification also limit their depth range.

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Interaction with humans

• Their shells are prized by collectors and artisans.
• They are also studied in evolutionary biology, biomechanics, and vision research.
• Aquarium displays fascinate visitors with a window into ancient ocean life.

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Fun facts

• Living nautiluses have changed little over 500 million years, true “living fossils”.
• Each nautilus has its own shell stripe pattern, like a biometric oddity.
• They glide using jet propulsion, not tentacle swimming like squid.

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