Got a new acro this weekend and noticed two crab hitchhikers. Don't have a pic yet but will try to get one. They are small, one about 1/4" wide at most the other smaller. Both are white with a black face. The black runs along the leading edge of the crab right across the eyes. Seem to only stay in the acro. Noticed this morning that one move over to another acro in the tank. Are these guys safe or do I need to get them out of there?? ID would be helpfull also.