Jellyfish with a snail shell?

[Fishkeeper]

We just got back from Port Aransas, and there were some strange animals washed up on the shore. They had lavender-colored snail shells, but the bodies looked nothing like snails. They looked like five or so clear bubbles, connected in a bean shape, with one end at the entrance of the shell. On the underside of the body was three rows of lavender paddle-things, kind of like the fins along the under side of a a shrimp's tail. The creatures came in several different sizes, always with an appropriately-sized shell. I also found some of the bigger ones, only about an inch long, without shells, but seemingly undamaged. If I put one of these in the water, it just floated, like a jellyfish. Ay ideas what these were?

[cardiocentric]

was this in FL?
purple sea snail perhaps?
http://www.google.com/imgres?num=10&um=1&hl=en&biw=1600&bih=744&tbm=isch&tbnid=wiWSxtHog44DhM:&imgrefurl=http://frozenly.com/2010/06/10-amazing-purple-animals/&docid=cjkppgUN6XC24M&imgurl=http://frozenly.com/wp-content/uploads/2010/06/purple-animals-02.jpg&w=468&h=366&ei=JvvfT7XKOIiQ9gTd5q2vDQ&zoom=1&iact=rc&dur=372&sig=103264307772777483873&sqi=2&page=1&tbnh=125&tbnw=167&start=0&ndsp=32&ved=1t:429,r:14,s:0,i:116&tx=140&ty=73

[Fishkeeper]

No, this was in Texas, but that's definitely what it was! So the foot-thing is mucus-covered bubbles, and these are carnivorous snails. They eat Portugese Man-'O-Wars, apparently. Those Man-'O-Wars really hurt if they tag you! I scooped one up on a shovel, and the very tip of one of its tentacles clipped me on the elbow. Owwww! Felt like a beesting. I would really hate to bump into all of one!