Nautiloidea - nautilus

Nautiloidea

There are six species of Nautiloidea; they have a snail-like shell which is divided by septa into gas-filled chambers, with only the last chamber being occupied by the animal, see Nautilus pompilus, below. A fully grown adult may have as many as 30 chambers. The empty chambers are buoyancy aids.

Nautiluses are found on the slopes of coral reefs in the Indo-Pacific at depths between 70 - 700m, any deeper and their shell would implode under pressure. The fossil record goes back 400 million years, and shells of modern species are similar to those found in the Jurassic about 200 million years ago. In the Jurassic some species had shells 50cm in diameter.

Nautiluses are hunted by humans using baited pots. They are hunted for both their shell and their meat. However, now they are protected, and their shells cannot be exported without a permit.

Nautilus pompilus, whole shell and half shell showing internal chambers

The septa are perforated in the middle, and through this a cord called the siphuncle passes (see the diagram below) and secretes gas into the empty chambers. The siphuncle is a cord of tissue running through the shell of the nautiloid connecting all the chambers with the body of the animal.

Nautilus anatomy

The mouth is surrounded by up to 90 tentacles or arms; all suckerless. Unlike other cephalopods nautiluses have simple eyes, sometimes termed "pinhole-camera eyes". Although their eyes are large they detect their prey using their sense of smell.

The hood acts as a cover or operculum when the animal withdraws into the shell. However, when the hood is closed the animal cannot breathe, so this only occurs in an emergency. The eyes and nervous system are relatively simple compared to the Coleoidea, and the eyes have no lens.

Nautilids lay eggs, which they place in crevices, that are large and have a hard coating. When nautiluses hatch from the egg they are around 3cm diameter, and are just miniature versions of the adults complete with shell. The eggs take around a year to hatch, and the hatchlings do not reach maturity for 15 years. After reaching maturity they can live for another 5 years.

All species are carnivorous.

Nautilus pompilus, Emperor nautilus, Common nautilus, Flame nautilus

Nautilus pompilus (above) is found in the Indo-Pacific region near the sea bed in waters up to 700m deep. During the night it rises nearer the surface to feed. It is about 24cm diameter across the shell when fully grown, and takes around 15 to 20 years to reach sexual maturity.

It swims backwards at about the same speed as a person swimming leisurely.

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