This minuscule, all-but invisible jellyfish was new to science in the 1960s, though its existence off northern Australia had long been known from a sickness afflicting unlucky swimmers in the summer months.
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The symptoms, including a rash and goose bumps, leading to intense back and abdominal pain, blinding headaches, high blood pressure and fits of coughing and vomiting, were called Irukandji syndrome.
But no victim saw the Irukandji, and no likely candidate had been caught in nets.
Marine biologist John Barnes devoted his life to tracking the creature down, and in 1961 captured a peanut-sized, transparent box jelly with four hairlike tentacles.
There was only one way to see if it was the culprit: he placed its tentacles on his skin - and felt the syndrome's effects. His find was named Carukia barnesi. There must be easier ways to have a species named after you....
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Main image: Carukia barnesi © Getty