An extremely rare crab was pulled from the Chesapeake Bay in June 2003, and is only second documented case of bilateral gynandromorphy among crabs in recorded history. The phenomenon known as bilateral gynandromorphy is when an animal carries characteristics of both males and females of their species. This condition has also been seen among moths, butterflies and lobsters.
Each half of the animal has all the characteristics of that sex, right down to split reproductive organs, and in the case of the blue crab, one blue (male) claw and one red (female) claw.
Source: Gender Bender