One of our readers, Gary S, found the thing above on the beach near La Barbera recently. He said he thinks it might be a Portuguese Man O' War. He also said he thought they could still sting even when dead. If WIkipedia is correct this is the case as I found the following quote:
"Detached tentacles and dead specimens (including those that wash up on shore) can sting just as painfully as the live organism in the water and may remain potent for hours or even days after the death of the organism or the detachment of the tentacle."
I found the photo below of a live one from the National Geographic website. It looks similar. So in the words of Hill Street Blues "Let's be careful out there".