That kind of jellyfish is a luminiscent jellyfish. Is one the four most typical jellyfish at Mediterranean sea.
On image, that jellyfish is stranded on a karst rock due to strong winds on the coast. It has been located at Calblanque natural park.
Aboout that jellyfish: "It measures about 20 cm in diameter at most. It has a more bulky mushroom-shaped umbrella, four oral tentacles and 16 marginal ones that can be deployed more than 20 m in length.
It is a translucent jellyfish of a pink color. In addition, it is covered with reddish brown warts on the surface of the umbrela, arms and tentacles. These are accumulations of cnidocytes, that is, the urticarial cells that shed the venom.
As its name says, the luminescent jellyfish glows in the dark. During the night it radiates a light that serves to attract its prey, but also as a reaction when it is disturbed.
It lives in deep areas of the pelagic, in the Mediterranean Sea and the Atlantic Ocean. But it approaches the coasts blown by the wind, especially in summer. It is one of the most poisonous species. Its sting is painful and causes intense irritation to the skin, which can cause blisters and ulcers." (Source: aquariumcostadealmeria.com)