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Sinking Aristotle’s Sailing Octopus

argonaut

A female argonaut (Argonauta argo) swimming close to the sea surface in the Sea of Japan. Photo: Julian Finn, Museum Victoria

By Julian Finn

By expertly manipulating air gathered from the sea surface, argonauts are able to control their buoyancy and traverse the world’s oceans at depth.

Dr Julian Finn is a Curator of Marine Invertebrates at Museum Victoria. This study has been published in the Proceedings of the Royal Society of London, B: Biological Sciences.

The full text of this article can be purchased from Informit.

In 300 BC, Aristotle wrote of a peculiar octopus that rises from the deep to sail on the ocean surface in a boat made of shell. Using two arms as sails and six arms as oars, it was said to have navigated the oceans of the world.

Two thousand years later, we now know that Aristotle’s fanciful octopus was in fact the pelagic octopus, named Argonauta by Linnaeus in 1758 on account of this sailing reputation. The boat, as Aristotle referred to it, is the beautiful white shell of the female argonaut. The sails are specialised webs used for secreting this shell.

Argonaut shells have long been familiar to coastal communities. Their image adorns artefacts dating back to Minoan civilisations (3000–1050 BC).

Despite this long familiarity, the elusive nature of the argonaut has kept much of their lives a mystery, including the true function of their shells. Recent wild observations of live argonauts have revealed that the shell is a precise hydrostatic structure employed by the female argonaut to obtain and accurately regulate buoyancy at varied depths.

Argonauts (family Argonautidae) are pelagic octopuses that live their entire lives without touching the sea floor. Due to morphological and molecular similarities, it is believed that the ancestors of the argonauts were bottom-living octopuses that departed the sea floor to invade the open ocean.

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The full text of this article can be purchased from Informit.