It is not very dangerous, but it is better not to touch it because it produces mucus with dispersed stinging cells, and entering in contact with this mucus causes irritations.
It entered the Mediterranean Sea through the Suez Canal, and is expanding through the Turkish coasts. In 2010 it was recorded at Malta, and so it reached the Italian waters. It is mostly found on sandy bottoms, but it can be present also on rocks.
How to identify it
The diameter can be 30 cm maximum, the jellyfish usually rests on the sea bottom, with the umbrella towards the bottom, whereas mouth and tentacles are upwards. For this reason, the species is called the upside down jellyfish. It has this posture because there are unicellular algae in its tissues, similar to the symbiotic algae of tropical corals, and they are also symbiotic with the jellyfish that, to make them function properly, has to expose them to light.