Argonaut (animal)

The argonaut is a type of octopus.

They live in warm ocean waters. Most octopuses stay on the sea floor. But argonauts live near the top.

The mothers make a thin shell. It is like a paper case. They use it to hold their eggs. The shell also holds a bubble of air. This air helps the mother float. It is a very special animal.

The argonaut is a special kind of octopus.

Most octopuses live on the dark sea floor. But argonauts live in the open ocean. They stay near the surface of the water. This way of life is called pelagic.

Female argonauts make a thin shell. People call this a paper nautilus shell. The female makes it using her arms. She uses the shell to hold her eggs. It also holds a bubble of air. This air helps her float in the water.

Male argonauts are very different. They are much smaller than females. A female can grow to 10 cm. A male is rarely more than 2 cm. The males do not make shells. They use a special arm to mate with the female. This arm is called a hectocotylus.

Argonauts can change their color to hide. They also use ink to escape from enemies. This ink can stop a predator from smelling them. Tunas and dolphins like to eat them. They live in warm waters all around the world.

The argonaut is a very special type of octopus.

These animals are pelagic, which means they live in the open ocean. Most octopuses stay on the dark seabed, but argonauts live near the surface. They are found in warm tropical and subtropical waters all around the world. People sometimes call them paper nautili because of their thin shells. However, they are only distant relatives of the true nautilus. The argonaut is a unique and amazing creature of the sea.

Female argonauts have a very interesting way of staying afloat. They secrete a thin, white eggcase using two large arms.

This eggcase is made of calcite rather than the aragonite found in most shells. The female uses the shell as a nursery for her eggs. She also traps a bubble of air inside the shell. This air bubble helps her maintain buoyancy near the surface. This system works best in the top 10 meters of the water.

Scientists once had many questions about how these shells form. Some people thought argonauts were like hermit crabs. They thought the octopuses just found empty shells from other animals. A marine biologist named Jeanne Villepreux-Power studied this in the early 19th century. She performed experiments to see how the animals grew. She successfully raised young argonauts and watched their shells develop. Her work proved that the females actually make their own shells.

There are big differences between male and female argonauts. This is called sexual dimorphism. Females can grow up to 10 cm long. They can also make shells that reach 30 cm in length.

Males are much smaller and rarely grow past 2 cm. Males do not have the special arms used to make shells. Instead, they use a modified arm called a hectocotylus to mate. This arm detaches and stays inside the female to help with fertilization.

Argonauts are part of a large world of ocean life. They eat small things like jellyfish, mollusks, and crustaceans. To protect themselves, they can change their color to hide. They also spray ink to confuse predators like dolphins or tuna.

Their name comes from ancient Greek myths about sailors. People thought they used their arms like sails to move. In reality, they swim by pushing water through a funnel. This is just like how other octopuses move through the sea.

Argonauts are a unique group of pelagic octopuses. Pelagic means they live in the open ocean rather than on the seabed. They belong to the genus Argonauta, which is the only living genus in the family Argonautidae. These animals are often called paper nautili because of the thin eggcases females create. However, they are only distant relatives of the true nautilus.

Unlike true nautili, argonauts do not have gas-filled chambers in their shells. Their eggcase is an evolutionary innovation used as a brood chamber and to maintain buoyancy.

To stay afloat near the surface, the female argonaut uses a clever mechanism. She captures a bubble of air at the water's surface and keeps it inside her eggcase. This air bubble provides buoyancy, helping her achieve neutral buoyancy. This system is most effective in the upper 10 meters of the water column. The eggcase is not made of aragonite like most shells. Instead, it is made of calcite, a mineral that forms a three-layered structure. It also contains a higher proportion of magnesium carbonate, at about 7%, than other cephalopod shells.

There is extreme sexual dimorphism in argonauts, meaning males and females look very different. Females are much larger, growing up to 10 cm with eggcases reaching 30 cm. The largest species, Argonauta argo, can produce an eggcase up to 300 mm long. In contrast, males rarely grow larger than 2 cm. Males lack the dorsal tentacles that females use to secrete shells. To reproduce, males use a modified arm called a hectocotylus. This arm transfers sperm into the female's pallial cavity and then detaches.

The female creates her ornate eggcase using two greatly expanded dorsal tentacles. These are her third left arms. The resulting shell is laterally compressed and has a double keel. It features two rows of alternating tubercles and ribbed sides. The eggcase can look like the shells of extinct ammonites. Once the eggs are deposited, the female takes shelter inside. She often keeps her head and tentacles protruding from the opening. If she is disturbed, she can retreat deeper into the shell.

History shows that our understanding of argonauts has changed over time. In the early 19th century, some believed argonauts were like hermit crabs. They thought the animals simply found and used abandoned shells. The pioneering marine biologist Jeanne Villepreux-Power disproved this hypothesis. Through her experiments, she successfully reared young argonauts. She observed their shells developing, proving they manufacture their own eggcases. Some researchers also speculate that argonauts may have evolved from using discarded ammonite shells before those animals went extinct.

Argonauts have specialized physical features for survival. Their beaks are distinctive, with a very small rostrum that is pinched in at the sides. This makes the beak narrower than most other octopuses. For feeding, they use their tentacles to grab prey like small crustaceans, mollusks, and jellyfish. They inject venom from a salivary gland to paralyze their food. To defend themselves, they can change color to blend in. They also eject ink to paralyze the sense of smell in attackers.

These animals are part of a complex marine food web. They are preyed upon by large animals such as dolphins, tunas, and billfishes. Their remains have even been found in the stomachs of fish like Alepisaurus ferox. The name "Argonaut" comes from Ancient Greek mythology. It refers to the sailors of the ship Argo. The Greeks also used the word "nautilus," meaning sailor. While people once thought they used arms as sails, they actually swim by expelling water through a funnel.