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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