I'm looking at the picture on my "big" computer. I think there's a possibility it's an honest to goodness fireworm. A Hermodice carunculata. Actually, I'm not sure why I'm saying "there's a possibility", as I'm really really really sure that's what it is. I would grab that whole disc out with a net, to ensure he doesn't bail. If I'm right, I would pay to have that shipped to me.