These unique creatures are also sometimes referred to as "paper nautiluses", because of the paper-thin eggcase that females secrete. The case is actually a chamber in which air is trapped to maintain buoyancy, and not the same structure present in a nautilus shell. Argonauts are pelagic octopuses, meaning that they live in the open sea, far from the ocean floor. They can be found in tropical and subtropical waters throughout the world
Like most octopuses, they have a rounded body, eight arms and no fins. However, unlike most octopuses, argonauts live close to the sea surface rather than on the seabed. Argonauta species are characterised by very large eyes and small distal webs.
Mankind has known about female Argonauts since ancient times, however because of the many differences between the males and females of the speices, we only became aware of the males in the late 19th century. Females grow up to 10 cm and make shells up to 30 cm, while males rarely surpass 2 cm. The males only mate once in their short lifetime, whereas the females are capable of having offspring many times with different partners over the course of their lives. I
Interestingly, the males lack the dorsal tentacles used by the females to create their eggcases. Instead, the males use a modified arm, the hectocotylus, to transfer sperm to the female. For fertilization, the arm is inserted into the female's pallial cavity, then is detached from the male. The hectocotylus when found in females was originally described as a parasitic worm!
After depositing her eggs into her eggcase, she will take shelter in it. Females are usually found with her head and tentacles protruding from the opening of the egg case, but they retreats deeper inside if disturbed. These ornate curved white eggcases are occasionally found floating on the sea, sometimes with the female argonaut clinging to it.
Argonauts use tentacles to grab prey and drag it toward the mouth. It then bites the prey to inject it with poison from the salivary gland. They feed on small crustaceans, molluscs, jellyfish and salps. If the prey is shelled, the argonaut uses its radula to drill into the organism, then inject the poison. They generally eat during the day.
Customary of octopuses, Argonauts are capable of altering their color. They can blend in with their surroundings to avoid predators. They also produce ink, which is ejected when the animal is being attacked. This ink paralyzes the olfaction of the attacker, providing time for the argonaut to escape. The female is also able to pull back the web covering of her shell, making a silvery flash, which may deter a predator from attacking.