Harmless to humans, but it is better not to touch it. It is probably harmless also for most fishes. Just as for Rhizostoma, it is often associated to young fish that use it as a shelter.
Very abundant in the Mediterranean Sea, expecially in bays. In 2009 it was more frequent in the southern part of Italy, showing a preference for warmer waters, but this was not confirmed in 2010 and 2011, since this species was very frequent throughout the whole Italian coast, especially in the second half of the summer.
How to identify it
One of the most beautiful jellyfish of the Mediterranean Sea. The umbrella can measure 30 cm in diameter, it is very rigid and roundish in its centre, where it has a reddish or yellow color. The external part of the manubrium is motile and pulsates vigorously. Under the umbrella, the manubrium resembles a bouquet of flowers, with blue-purple buttons, inserted into stout arms. Some tentacles, also terminating with blue buttons, are inserted on the manubrium. Cotylorhiza can have symbiotic microalgae that live in its tissues, just as those of tropical corals. Functionally it is a “plant”, even if it can feed on zooplankton.