I had one of those crabs for months before I ever saw him. The way I see things in my tank that I did not buy is: guilty until proven innocent. I took my out and took it to the pet store. My friend took it off me for store credit. I gave it up cause I was not sure what it was, but as far as I know it was harmless. Every time I saw it it was just eating live rock. But I agree with reefymark, his pinchers are flat. If you feel unsure about him, take him out for your sake, but Imho he is harmless, but I do agree with you, he is ugly and creepy looking. The red eyes do look EVILLLLLLLLL.