This picture was taken on the shores of Hartenbos, South Africa. It's known as "Bluebottles" down there.
I've seen them down in Florida too. They call it a "man-o-war" in the US.
I have been stung a few times, it is quite painful.
Excellent shot, in France it's called "galère portugaise" or "physalie". Scientific name is Physalia physalis
What is that?