Nautilus pompilius Linnaeus, 1758

Nautilus pompilius, commonly called the Chambered Nautilus, is the most common Nautilus and the only Cephalopod with true external shell.

Nautilus pompilius pompilius Linnaeus, 1758 - called the Emperor Nautilus, this larger subspecies is found in the Andaman Sea east to Fiji and southern Japan south to the Great Barrier Reef. Nautilus pompilius suluensis Habe and Okutani, 1988 - this smaller subspecies is restricted to the Sulu Sea in the southwestern Philippines.

Sexual maturity: At 15-20 years of age. Fertlisation: Internal. 4 tentacles of male transfer spermatophore to female's mantle wall where it disintegrates to release sperms. Eggs: Oblong in shape and about 1.5 inches in length (Brusca and Brusca 1990, Dybas 1994).

Length: 150mm-180mm. Mean size about 165mm. Total weight: 850g.

Smooth thin shell with small umbilicus, exogastric spirals, with many chambers varying in number depending on the age of the mollusc - about 30 in adults, a siphuncle releasing gas to keep the nautilus in upright position, a tough hood, 90 small suckerless tentacles below the hood, a funnel containing two separate lobes, eyes with no cornea or lens, and variable colouration which generally comprises irregularly radiating brown stripes that extend from umbilicus to venter. Also, shells show countershading with lighter bottoms and darker tops.

Countershading of shell helps this species escape from predators - when seen from above, it blends with the light, and when seen from below, it blends with the darkness of the sea. With primitive pin-hole camera-like eyes, this mollusc depends on chemotaxis through a pair of rhinopores and olfaction to hunt prey.

Feeds on fish, crabs and carrion (Attenborough 1979, Morton 1979).

Marine: Usually near the bottom of shores and coral reefs, upto a depth of 500m, except in the night when they rise closer to the surface.

Not evaluated by IUCN Redlist.

A major threat to this species comes from over-fishing by humans.

Listed in CITES: No. Listed in Wildlife (Protection) Act: Yes. Schedule: 1 Appendix: Part IV(B) Mollusca

Used in research. Shells also sold as such, polished or made into different kinds of handicrafts.