A Leatherback sea turtle was found washed up on Anglesey on Tuesday after the winds from Hurricane Ophelia.
The turtles are normally found in tropical waters such as those off the northeast coast of South America or French Guiana.
It was first discovered by a Holyhead coastguard near Rhosneigr.
Rod Penrose of the UK Cetacean Strandings Investigation Programme said only the top shell, made of skin and bones, was left of the rare turtle.
Frankie Hobro, director of Anglesea Sea Zoo, said that Leatherback turtles come to the seas off north Wales each summer to feed on swarms of jellyfish from April to September.
Earlier this month, Sea Trust Wales director Cliff Benson said this had been a “really epic year for jellyfish”, including record numbers of Portuguese man o’ war that have washed up in Wales this year.
Mr Penrose said that this was the eleventh Leatherback to wash up in Wales this year.
Leatherback turtles are a critically endangered species.