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A native of the tropical Pacific, this cousin of the octopus is a living link with the past—little changed for more than 150 million years. Its simple eyes may see no more than the difference between dark and light, but the nautilus uses its more than 90 tentacles to touch and taste the world. A nautilus’s tentacles—unlike those of other cephalopods—have grooves and ridges that grip food and pass it into the nautilus’s mouth. A parrotlike beak rips the food apart, and a radula (found in most molluscs) further shreds the food.
To avoid predators by day, a nautilus lingers along deep reef slopes, some as deep as 2,000 feet (610 m). At night, a nautilus migrates to shallower waters and cruises the reefs, trailing its tentacles in search of food.
A nautilus swims using jet propulsion—it expels water from its mantle cavity through a siphon located near its head. By adjusting the direction of the siphon, a nautilus can swim forward, backward or sideways.
Collectors seek out nautilus shells, which are beautiful with their mother-of-pearl lining and reddish-striped, cream-colored exterior. In the past, beachcombers gathered only shells that had washed up onto the beaches, but now demand for perfect shells is encouraging deep water trapping of nautilus. Since these animals mature late and produce few offspring, shell collecting results in a significant decline in nautilus (and other mollusc) populations. For this reason, the aquarium doesn’t sell sea shells in its gift shops.
A newly hatched nautilus wears a shell divided into four small chambers. As a nautilus grows, it gains more living space by building new chambers connected to the old ones; adult shells have 30 chambers. To control its buoyancy, a nautilus pumps fluids in and out its shell chambers, which are connected by tubes called “siphuncles.”
Nautilus populations tend to be 75% males and 25% females. Reasons for this are not yet clear.