Named for the sailors of Greek mythology, argonauts – also known as paper nautili – are a unique group of shelled octopuses (and can’t sail)
The common name ‘paper nautilus’ refers to the paper-thin shells secreted by female argonauts, a unique evolutionary innovation of this unusual genus of pelagic octopus.
Although they share a similar name, argonauts are only distantly related to the ‘true’ nautiluses. Unlike their hard-shelled relatives, the argonaut’s shell is actually an eggcase, secreted by the female argonaut who then moves inside it to care for her brood.
The shell is also used to trap bubbles of air which the animal uses to maintain neutral buoyancy, enabling the paper nautilus to drift in the current near the surface of tropical and sub-tropical waters, where they are sometimes encountered during blackwater dives.
The four extant species exhibit extreme sexual dimorphism – females grow up to five times the length of the males and secrete shells that can reach 30cm in diameter, whereas the males rarely exceed 2cm in length.
Males mate only once before dying, using a special arm called a hectocotylus, which he detaches and which can move independently to transfer sperm to the female. Due to their short lifespan and size, male argonauts were not scientifically described until the late 19th century.
Argonauts feed during the day, using their tentacles to drag small crustaceans, molluscs and jellyfish to their mouths and biting them to inject the prey with venom. They can produce ink to deter predators and females can pull back their shells, creating a silver flash to confuse their attackers.
The name ‘nautilus’ derives directly from the Greek nautílos, which translates as ‘sailor’. The name was first used to describe them as it was believed they used two of their tentacles to sail through the water, however, they ‘swim’ like other species of octopus, using a form of jet propulsion created by rapidly expelling water from their siphon, or ‘funnel’.
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