"It was upside down - it looks like a big leatherback turtle, " he said.
BBC: NEWS | UK | Wales | South West Wales | Dead turtle washed up on beach
The shell is flexible and covered in a black leathery skin - hence the name leatherback.
Even if the leatherback survives the hatching process, it faces many more dangers on its journey.
The Harlech leatherback has been put on display at the National Museums and Galleries of Wales in Cardiff.
BBC: NEWS | UK | Wales | South West Wales | Dead turtle washed up on beach
Leatherback turtles weigh around 600kg (95st) and their shells can be up to two metres (6ft 7in) long.
Reported sightings of leatherback turtles are increasing off Wales, with the reptiles thought to be drawn by high numbers of jellyfish.
BBC: Leatherback turtle sightings up in west and north Wales
Last August thousands of leatherback eggs and hatchlings were crushed by bulldozers moving waterlogged sand from key nesting areas.
Experts are also hoping it will lead to a better understanding of the endangered leatherback turtle, which feeds on jellyfish.
Experts said it was a Leatherback turtle and was probably fully grown.
BBC: NEWS | UK | Wales | South West Wales | Dead turtle washed up on beach
Weighing more than 700 kilograms and reaching more than 1.7 meters in length, the leatherback turtle is the world's largest marine reptile.
Dr Richardson said there had been high numbers of jellyfish - the food source of the leatherback - reported in the Irish Sea this year.
BBC: Leatherback turtle sightings up in west and north Wales
As well as being a nesting site for the leatherback turtle, the area is home to more than 860 different types of flora and fauna.
In 1980 the worldwide leatherback population was estimated at around 115, 000.
One study in 2004 estimated leatherback turtles had only a 50 percent chance of avoiding being accidentally snared by a deep sea fishing line each year.
"There is the problem of plastic bags and balloons which have been ingested by leatherback turtles off Cardigan Bay when mistaken for jelly fish, " said Ms Bell.
Puerto Rico has introduced a new law protecting a swathe of the island's coast that has become a major nesting site for the world's largest turtle, the leatherback.
Although the turtle found at Pendine was big, it came nowhere near the size of the world's largest leatherback turtle which was washed up on a north Wales beach in 1988.
BBC: NEWS | UK | Wales | South West Wales | Dead turtle washed up on beach
But with the help of some high-tech tracking devices, a fan-friendly Web site and a little star power, conservation officials are hoping a contest among 11 leatherback tortoises will raise awareness, and some money, for the critically endangered species.
At the Gamba protected-area complex, on the coast of Gabon, patrolling rangers make daily logs of deposits of flotsam from the industrial world that has arrived on their remote Atlantic beaches at the same time as they record the comings and goings of the local leatherback turtles.
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