Common Name: “nautilus” (pl: “nautiluses” or “nautili”)
Families: 1 - Nautilidae
Anatomy: Smooth external shells with internal chambers, 50-90+ tentacles, toothed radula within parrotlike beak
Diet: crustacean molts, hermit crabs, carrion
Habitat/Range: Indo-Pacific ocean, at depths of several hundred metres
Evolved in: Order Nautilida in the Devonian, Family Nautilidae in the Triassic (230 million years ago)
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During the Middle Devonian, Nautilus species were more diverse, and their shells were more varied than those found in species of living Nautilus, ranging from curved (cyrtoconic), through loosely coiled (gyroconic), to tightly coiled forms, represented by the Rutoceratidae, Tetragonoceratidae, and Centroceratidae. Only a single genus, Cenoceras, with a shell similar to that of the modern nautilus, survived the Triassic extinction, at which time the entire Nautiloidea almost became extinct. They diversified again, but never reached the extent of diversity they had before the Triassic extinction. The nautilids were not as affected by the end Cretaceous mass extinction as the Ammonoids that became entirely extinct, possibly because their larger eggs were better suited to survive the conditions of that environment-changing event.
Nautiluses are the sole living cephalopods to have external shells. They can withdraw completely into their shell and close the opening with a leathery hood formed from two specially folded tentacles.
The nautilus has the extremely rare ability to withstand being brought to the surface from its deep natural habitat without suffering any apparent damage from the experience. Where fish or crustaceans brought up from such depths inevitably arrive dead, a nautilus will be unfazed despite the pressure change of as much as 80 standard atmospheres (1,200 psi).
Nautiluses have a seemingly simple brain, lacking the large complex brains of octopus, cuttlefish and squid, and had long been assumed to lack intelligence. But recent experiments have shown not only memory, but a changing response to the same event over time.
In a study in 2008, a group of Chambered Nautiluses (Nautilus pompilius) were given food as a bright blue light flashed until they began to associate the light with food, extending their tentacles every time the blue light was flashed. The blue light was again flashed without the food 3 minutes, 30 minutes, 1 hour, 6 hours, 12 hours, and 24 hours later. The nautiluses continued to respond excitedly to the blue light for up to 30 minutes after the experiment. An hour later they showed no reaction to the blue light. However, between 6 and 12 hours after the training, they again responded to the blue light, but more tentatively. The researchers concluded that nautiluses had memory capabilities similar to the "short-term" and "long-term memories" of the more advanced cephalopods, despite having different brain structures.
Female nautiluses spawn once per year and regenerate their gonads, making nautiluses the only cephalopods to be able to breed more than once in their lifetime.
Nautiluses may live for more than 20 years, which is exceptionally lengthy for a cephalopod, many of whom live less than 3 even in captivity and under ideal living conditions. However, nautiluses typically do not reach sexual maturity until they are about 15 years old, limiting their reproductive lifespan to often less than five years.
The osmeña pearl is not actually a pearl, but a jewellery product derived from the iridescent inner layer of the nautilus shell. Nautilus shells are also sold whole, carved as souvenirs, or historically used to make items such as lamps and cups. However, these are not simply shells that wash ashore; the animals are killed for the shell. The low fecundity, late maturity, long gestation period, and long life-span of nautiluses make them vulnerable to overexploitation, and high demand for their ornamental shells is causing population declines. In 2016 all species in the family Nautilidae were added to CITES Appendix II, regulating international trade, though in some places they can still openly be found for sale in tourist areas. The best way to combat nautilus population decline is to stop the demand for these shells.
