The Crambione Cookii has not been seen since 1910 but was spotted off Queensland, Australia, by Puk Scivyer, who chanced upon the animal while releasing a rescued sea turtle.
The aquarium worker said: ““As soon as I saw it I realised it was a species I’d never seen before.
“But to then discover I was the first person to see this species in over a hundred years was just incredible.”
Jellyfish expert Dr Lisa-Ann Gershwin was called in to identify the unusual ocean-dweller, after it was captured in waters off Sunshine Coast.
It is now being cared for at the UnderWater World aquarium in Queensland.
Scientists are baffled how the 20in pink jellyfish - which has a sting so powerful it can be felt in the waters surrounding the creature – escaped notice for so long.