Crystal jellyfish usually live in the northern Pacific and are a rare species in Welsh waters. At first glance they could easily be mistaken for moon jellyfish, but lack the four rings and are almost transparent. They can reach up to 10 inches in diameter, have a mild sting and are bioluminescent when disturbed, producing a green light.
The image shows the underside (left) and the top of the bell (right).
Found at : Quarry Beach, Llyn Peninsula