This wasn’t the first thing that sprung to mind when I thought of jelly but I didn’t feel like making one and a search in my 50k archive came up with nothing .. except a jellyfish! Shot this guy in Barbados a few years back, it frightened the hell out of me and I didn’t go for a real swim in the sea after that.
It is a Portuguese man o war, or blue bottle as we call them here in Australia. Don't touch it, even in this state it can give you a sting that is quite nasty. https://en.wikipedia.org/wiki/Portuguese_man_o%27_war
it could be a Portuguese Man of War?
I wouldn't have gone in the water either
https://en.wikipedia.org/wiki/Portuguese_man_o%27_war