Overview
The Crusty Nautilus (Allonautilus scrobiculatus), also known as the king nautilus, is one of the rarest, most enigmatic marine organisms on Earth. Distinct from common nautilus species, this primitive cephalopod is distinguished by an extraordinary thick, velvety, and hairy outer shell coating (periostracum) and an unusually wide central umbilicus, surviving in cold, deep oceanic waters surrounding remote islands of Papua New Guinea.
Biology and Physical Characteristics
Allonautilus scrobiculatus possesses a planar-spiral shell divided internally into numerous gas-filled chambers linked by a living vascular tube called a siphuncle, which regulates internal buoyancy via osmotic water transfer. Unlike the smooth, glossy shell of Nautilus pompilius, the shell of Allonautilus is enveloped in a thick, fibrous, moss-like periostracum that feels rough and slimy to the touch, providing camouflage against rocky abyssal drop-offs. The creature extends up to 90 slender, suckerless tentacles equipped with adhesive tactile ridges to manipulate food and navigate rocky terrain.
Behavior and Ecology
Inhabiting depths between 500 and 1,300 feet (150–400 m) where water temperatures remain between 9°C and 16°C, the crusty nautilus cannot survive in warm surface waters above 25°C. By day, it shelters along sheer deep-reef walls; under cover of darkness, it uses jet propulsion via its muscular hyponome funnel to cruise slowly above benthic sediment, deploying highly sensitive chemosensory tentacles to detect the scent of decaying carrion, molted lobster carapaces, and scavenging crabs from hundreds of yards away.
Conservation and Human Impact
Assessed as Data Deficient by the IUCN and protected under CITES Appendix II, Allonautilus scrobiculatus has one of the smallest geographic ranges of any cephalopod. Because nautiluses take up to 15 years to reach sexual maturity and lay very few eggs, populations are exceptionally vulnerable to overexploitation by targeted deep-water cage trapping for the international ornamental shell trade, as well as rising deep-sea temperatures linked to climate shifts.
Interesting Factoid
After being first described in 1786 and photographed alive in 1984 by marine biologist Peter Ward, the elusive crusty nautilus was not seen alive again in the wild for over 31 years until a rediscovery expedition located it off Manus Island in 2015!
Last updated: October 2026