Video: Argonaut

In celebration of a truly unique species of octopus, here's a neat little video of an argonaut doing its thing out in the wild.


Filmed by Yasushi Okumura of Japan Underwater Films


To learn more about this incredible species of octopus, check out the earlier post, Species: Argonaut.

Species: Argonaut

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.

Ancient Octopus Mystery Resolved

By Rosalind Pidcock
Science reporter, BBC News

May 19, 2010


Trapped air in the shells of rare octopuses is the key to their survival in the deep sea, say scientists.

Females of the argonaut family (Argonautidae) release trapped air from their shells to control very precisely their movement through the water.

This ability has puzzled naturalists for over 2,000 years, dating back to observations made by Aristotle in 300 BC.

Research published in the Royal Society journal, Proceedings B, finally explains why it may have evolved.

The Australian researchers describe how the mechanism enables the creatures to conserve energy, avoid predators and protect eggs during the brooding stage.

The study, led by Dr Julian Finn of Museum Victoria in Melbourne, is the first to observe directly how this unique species of octopus captures air at the sea surface and uses it to its advantage.

"It wasn't until I actually got an argonaut in the water that I really saw the true marvel of these animals," said Dr Finn.

Unlike any other species of octopus, the female argonaut, which can be up to 50cm (20 inches) in length, makes itself a paper-thin shell. It secretes this shell, made of calcium carbonate, from two web structures on the sides of its body.

The males are much smaller, typically only a centimetre in length, and do not produce shells.

Mythical Creatures
Air pockets have been observed before within the shells of both wild and captive argonauts, also known as "paper nautiluses", but their origin and purpose has until now been a mystery.

"This mythical story began around the time of Aristotle that the argonaut female actually lived in the shell and raised those webs as sails as she sailed across the ocean," explained Dr Finn.

The new findings show that the female argonaut takes in air at the sea surface through a funnel as it rotates its shell anti-clockwise. It then seals off an air pocket in the top, or apex, of the shell using a second webbed pair of tentacles.

As it dives to depths of up to 750m (almost half a mile) below the surface, it adjusts the amount of air in its shell to match its own density with that of the seawater, keeping it "neutrally buoyant" and enabling it to swim effortlessly.

This contrasts with most other cephalopods - the class of animals that includes octopuses, squid and cuttlefish - which expend vast amounts of energy to maintain their position.

Underwater Control
The female argonaut can also counteract the considerable weight of its eggs, which it releases into its shell during the reproductive period, to carefully avoid bumping them on the sea floor.

By keeping a safe position in mid-water, argonauts can also steer clear of disturbance by surface waves and predators from above, such as birds.

Once believed to hinder the females, it is now thought that argonauts evolved this remarkable mechanism from ancestors that lived on the seafloor, allowing the species to expand its range into mid-depths.

"The female argonaut knows exactly what she was doing. Underwater she was completely in control," added Dr Finn.