Flamingo tongue snail. This creature is an obligate feeder on coral polyps and is most often found munching on the branches of gorgonians in the caribbean.
One of the local LFS's got one in once, and wasn't sure what to do once he'd identified it. I'm with Matt on the gorg ID. Also the porites looks like the one I have in my tank, which is just a generic porites sp.
I kept one of these Cyphomas for about 1 1/2 years. I just put a piece of sea whip in the tank for it to munch on, and that kept it going for a long time. In my experience, they don't seem to destroy their host gorgonians very fast, and someone good at growing gorgonians may could set up a system that will sustain one or two of these without having them kill the colony they live on.