ca. 100; see text
A fiddler crab, sometimes known as a calling crab, may be any of approximately 100 species of semi-terrestrial marine crabs which make up the genus Uca. As members of the family Ocypodidae, fiddler crabs are most closely related to the ghost crabs of the genus Ocypode. This entire group is composed of small crabs – the largest being slightly over two inches across. Fiddler crabs are found along sea beaches and brackish inter-tidal mud flats, lagoons and swamps. Fiddler crabs are best known for different sized front claws, with one claw usually much larger than the other.
The Florida stone crab, Menippe mercenaria, is a crab found in the western North Atlantic, from Connecticut to Belize, including Texas, the Gulf of Mexico, Cuba and the Bahamas that is widely caught for food.
Uca pugilator, the sand fiddler crab is a species of fiddler crab that is found from Massachusetts to the Gulf of Mexico. It lives in burrows in coastal and estuarine mud-flats, and can be extremely abundant. It can be differentiated from its congeners U. pugnax and U. minax by the smoothness of the inside of its claws. One claw is larger than the other, and can be much larger than the crab's body, at up to 41 mm (1.6 in) long.
The carapace is square in shape, tapering slightly to the rear; it can reach a width of 25 millimetres (0.98 in), but is typically up to 21 mm (0.83 in) wide and 14 mm (0.55 in) long. The space between the eyes is much shorter than the eyestalk. The males have one extremely enlarged chela (claw), which they use to claim their territory and fight with other males. The claw can be much larger than the body, at up to 35 mm (1.4 in) long, or exceptionally up to 41 mm (1.6 in) long. It is common for males to lose claws in the battles. When this happens, the claw regenerates and the opposite side begins to enlarge. Fiddler crabs are right or left clawed. The inside of these claws are also very smooth, unlike its other close relatives Uca pugnax and Uca minax.