I found this creature floating in the Mediterranean Sea, probably dead. I tried looking it up in the Marine Species Identification Portal but I couldn't find anything like that. It looks like some kind of jellyfish or hydrozoan.
This is a blue button jellyfish! they eat zooplankton and are usually found drifting along on currents
they aren't true jellyfish and just like a jellyfish have no blood, brain or nervous system. they aren't usually toxic enough to hurt but can cause irritation to the skin.
they live in warm waters off of Europe and in the golf of Mexico and the Mediterranean.
they are hermaphrodites and have both male and female reproductive parts. they lay eggs which turn into polyps
here is a website I found all about them as I'm not extremely knowledgeable on this species.