The chambered nautilus is a small to medium-sized aquatic invertebrate living in the waters around Asia and Australia. These weird animals are mollusks, related to octopuses, squids, shellfish, and snails. Nautiluses are a family of animals belonging to the Class Cephalopoda. This class contains animals such as cuttlefish, squid, and octopus. This specific species of nautilus is divided into several chambers. The outer chamber contains all of the animal’s organs, while the multiple inner chambers contain gasses that control the animal’s buoyancy. As you can see on the right side of the picture above, nautiluses have many tentacles. They can have more than ninety of these tentacles, but unlike octopuses and squids, the nautiluses do not have suckers on their tentacles. Another difference between these animals and octopuses and squids is that nautiluses do not have good eyesight. In fact, their eyes do not have lenses to focus with! One similarity between these animals and the other mentioned cephalopods is that all of them have beaks for mouths. The word nautilus comes from the Greek word nautilos meaning sailor. The Latin word nauta, similar to the word nautilus, also means sailor.
Nautilus shells can be up to eight inches (20.3 cm) across, but they are normally smaller. The average shell size is 6.5 inches (16.5 cm). Males are slightly larger than females. The total weight of a nautilus including its shell is about 1.9 pounds (850 g), but remember that they can change their weight using different gasses.
The chambered nautilus lives in tropical waters from Japan to the Great Barrier Reef of north-eastern Australia. These animals normally inhabit the places where coral reefs descend into deep ocean. During the day, these nautiluses live in the cool waters from 900 to 2,000 feet (275-610 m) below the surface. At night, they ascend to shallower waters where they feed. At this time of day, they normally inhabit waters between 300 and 500 feet (90-150 m) below sea level.
The bad eyesight of the chambered nautilus does not allow it to find prey with its eyes. Instead it must use good sense of smell to find prey. These animals eat fish, crabs, and carrion. Sometimes they will even eat the exoskeletons of animals that have molted recently. In order to find food, it uses the chemical sensors on its tentacles to detect traces of predators or prey. It will then blow water out of its siphon to clear the sand away from the prey. Because it takes so little energy for a nautilus to swim, it only needs to eat about once each month.
Nautiluses swim using a siphon that is normally hidden by its tentacles. They pump water out of this to propel them backwards. Wait, backwards? Yes, since the siphon points forward, the nautilus goes backwards when water is pumped out of the siphon. The nautilus can then not see at all where it is going and frequently bumps into obstacles. Sometimes these animals will curl the siphon backwards so they can swim forwards, but because of their poor eyesight, they still are quite clumsy. Sometimes they will also use their tentacles to crawl along the reef. Click here to see a video about the chambered nautilus including it swimming backwards.
Status, threats, and protection
Neither the IUCN nor CITES have ranked the status of the chambered nautilus. The shell of all nautiluses is highly prized for decorations, and the chambered nautilus is the most common species sold. Traders in Fiji, Indonesia, and the Philippines capture these animals using baited traps. Concern has been expressed for these animals because they reproduce slowly, and in Indonesia it is now illegal to export them. Some natural predators include octopuses, sharks, sea turtles, and triggerfish. When threatened, the nautilus will retreat into its shell and close the opening with the leathery hood seen right above the nautilus’s eye and tentacles in the picture above. This defense mechanism does not work against some animals such as sharks, sea turtles, and octopuses which can bite through the nautilus’s shell.
Mating, eggs, and young
Nautiluses will reproduce once each year after they have matured. The male uses four modified, fused tentacles called the spadix to fertilize the female. The female then deposits about a dozen eggs singly or in small groups. She does this throughout the year, but only lays twelve eggs through this whole time. These eggs are about one inch (2.5 cm) in length, making them some of the largest invertebrate eggs. The eggs incubate between nine months and three years. Newly hatched chambered nautiluses are about the size of a U.S. quarter. They feed on shrimp and other small prey. At this time they only have four chambers, but this number grows over their fifteen years of life.
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- Chambered nautilus – Public domain
- Mystery animal – Karelj