I think your original question has been answered but from what little I have read about red claw crabs, they could be a danger to your shrimp (or possibly the pygmy corys someone suggested) and need a way to get out of the water into the air. They also seem to love to climb and if there are any openings in your cover, will most likely leave the tank. One article I read also said that you should only keep one as they can be very aggressive toward their own species. They are also best kept in brackish water. Bear in mind, this is only from what I have read and not from personal experience.