Can someone please help me identify this? Would have hitchhiked on my TBS live rock two years ago, but this is the first time I’ve noticed it. I would say it’s about a quarter of an inch. This is its underside (it was stuck on the back side glass at first, but I removed it and it is resting on the bottom glass for this picture). It didn’t really look like a normal snail shell, but has a hard surface on the creature’s back side that looked rock like. Also, it isn’t sucking its body into its “shell”, which is what a snail would typically do when not attached to anything. Any ideas?