argonaut
/ˈɑːɡ(ə)nɔːt/
noun
A small floating octopus, the female of which has webbed sail-like arms and secretes a thin coiled papery shell in which the eggs are laid.
Genus Argonauta, order Octopoda
Also called paper nautilus
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Here Jason was in his ignorance, thinking argonauts were some group of adventurous sailors out of ancient Greece. Instead he finds they are little octopus critters with a shell. [Wasn't there even a movie?]