Vemetid snails,
Awww crap. We have these things in our tank too. Wasn't really a problem until I've been kinda overfeeding the tank to try and get the Hippo to eat. They seem to be popping up a lot here lately. Ours are rather small...the part that attaches to the rock (or whatever) looks somewhat like a coiled up snake with a hard calcerous tube sticking straight up out of the middle. There is a mucus type thread that comes out of the tip which seems to aggrevate whatever coral it touches.

Not being sure what they were, I've been leaving them up to now. Just went and broke one of them off the coral it had attached itself too - sure enough, there was a *very* small, white snail like looking creature inside the tube. I guess I've got some work ahead of me - finding and disposing of them. :P

Wendy