Id hitch hiker (w/pics)

Bri Guy

New member
Ok this is a small flat disc, in the rock pic, it's to the left of the only hole in the rock in the middle. I broke it in half and there were no guts or anything. They seem to be made up of calcium, like most things in the sea, and I would think that it was a piece of snail shell (like there door that they close) but I know that its not because I see them move around, even on the glass, not very fast but they are alive. Any clues?

Thankx And by the way, are these guys bad or just calcium users.