|Image via Wikipedia|
Beneath the float is the beautiful bright blue hydroid colony. They look quite a lot like jellyfish tentacles but you have to remember that the round float isn't a body, it's more like a life ring. If I was drifting along holding onto a life ring for dear life, I wouldn't want people to focus their attention on the life ring because the guy hanging on could probably grow back or something! It would be all the worse if I wasn't the only one hanging on. In all honesty though, this is a Cnidarian composed of loads of tiny polyps, I have no idea what could grow back and what couldn't!
In any case, the Blue Button still has those infamous stinging cells, also known both as nematocysts and cnidocytes. They're pretty much harmless to humans, used instead to kill and capture tiny bits of food such as plankton, larval fish or miniscule eggs. This is in fact done by some of those tentacles, before they feed the hungry mouth beneath the float. Other tentacles then go about digestion, while others will eventually begin the very important task of reproduction.
Not a particularly well known creature, but I can't help but feel that's it's a wondrously beautiful one.