What’s A Nautilus?


The Nautilus is thought to have been swimming in the planet’s oceans for 500 million years, a long history that has earned them the nickname ‘the living fossil’. They live in chambered shells, which can become as big as 20 cm in length. The Nautilus shell has two main regions. The front or outermost region is the living chamber, which has the soft body of the Nautilus. Nautilus live inside their coiled shell for protection, but as they grow the Nautilus creates a new living chamber, leaving an empty chamber behind. It is these empty chambers that create the second region of the shell, which looks like a series of empty rooms that form the shape of a spiral. Adults can have up to 30 chambers, as the shape of the shell winds down in a coil, the chambers get smaller and smaller.

x-ray of a nautilus
x-ray of a nautilus

Description: Nautilus are cephalopods, which means they are related to octopi, squid and cuttlefish. They have a beautiful shell with brown and reddish stripes that looks like pearl on the inside. Their shells are so strong they can withstand pressure at depths of nearly 2,600 feet beneath the surface of the ocean. Under the hood or front of the shell you can see90 small tentacles and primitive eyes. Nautili have really poor vision but an incredible sense of smell.

Habitat: This amazing animal can be found in the Western Pacific Ocean off the coasts of the Philippines, Papua New Guinea, Fiji and Australia. They live deep in the ocean, 900-2000 feet down, coming up to shallower water at night to hunt. Nautili live at ocean depths that we know little about. The Nautilus is an example of a species that makes you think about the incredible diversity of habitats and life forms on Earth, many of which are still largely undiscovered.

nautilus diagram
nautilus diagram. Photo Credit, Commonwealth of Australia

Movement: Cephalopods, like the Nautilus, swim by pushing water in and out of their chambered shell through a special tube called a siphon. They use this jet propulsion to move quickly through the water, similar to how jets use the movement of air through their turbines to speed up. Nautili stay afloat in the water by using two different mechanisms; the first uses gas, while the second relies on osmosis.

Nautilus tentacles and siphuncle
Nautilus tentacles and siphon, Photo Credit: Flickr User, Dremsen

The Nautilus can release gas into the empty chambers in their shell through a tube called a siphuncle. The gas helps keep the Nautilus upright and buoyant, or afloat. Nautili can also take in water into their living chamber through the sides of their siphuncle, they use this water to absorb salt into their blood. This salt leaves less water in their blood, while their living chamber has a higher concentration of water. By adjusting the flow of water between their blood and living chamber through osmosis they create different concentrations of water. This special ability also helps the Nautilus to stay afloat. These features make the Nautilus incredibly well designed for moving through the water, so much so that submarines have been named after them.

Lifecycle: Once a year, females will deposit the fertilized eggs onto rocks in shallow water. Females then incubate and care for the eggs for nine months to a year. When hatched the newborn Nautilus will be 2.5cm in diameter. The Nautilus lives 15-20 years.

Predators: Octopus, sharks, triggerfish and turtles

Diet: Nautilus use their sense of smell and tentacles to find prey, and they eat mostly crustaceans and carrion (dead animals).

two nautilus swimming coral reef

O’Dor RK and DM Webber (1991). Invertebrate athletes: trade-offs between transport efficiency and power density in cephalopod evolution. Journal of Experimental Biology 160:93-112.
Ward PD (1987). The Natural History of Nautilus. Allen and Unwin, London.
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