I found 3 of these guys in there and took them to my LFS and they tossed them in their display tank. He said he had never seen one before. Very ugly looking and somewhat mean. They would raise up if you got to close to them. I havent seen anymore in the last couple days so hopefully thats all of them.
raising up in a defense position is no indication of a crabs temperment. he just doesn't like a gigantic monster 10,000 times the size of him, getting too close. i can't say that i blame him.
look at the japanese. every time a giant lizard or turtle comes to town, they call the army! poor godzilla!