Nah, he's completely harmless. He stays in it or under it pretty much always. When I first got him, he traveled around a bit before he ended up there. I didn't actually know I was getting an anemone crab....I ordered a "porcelain crab" because I had a non-anemone-hosting porcelain crab before which was very cool, and then this one just sort of ended up hosting the carpet.
jds