Mudflat fiddler crab

Uca rapax

Family Ocypodidae - Fiddler and ghost crabs

Carapace oval, narrower posteriorly; anterior lateral margins slightly curved; color greenish brown or greenish blue on carapace, claws white with yellow or orange tinge, mottled brown spots on back of palm; females with very small claws of equal size; males with 1 oversized claw with short tubercle ridge on palm, ridge relatively high, tubercles stop at top of ridge, do not continue to other side of palm; no enlarge tooth or spine on inner surface of carpus (segment next to claw) on enlarged claw in males; palm of male major claw mostly smooth, sometimes with a few small flat tubercles; crest on end of immovable finger of major claw with 3-4 tubercles, the immovable finger is slightly curved inward; walking legs with hairs on dorsal and ventral margins; pile of short bristly hairs (seen with magnification) on the dorsal margin of its 1st 3 walking legs; area between orbits narrow, less than 1/3 of the frontal width of the carapace.
Similar Species
Most resembles the Atlantic marsh fiddler, U. pugnax, but the Atlantic marsh fiddler differs in these ways: the immovable finger on the male major claw is straight or with a slight downward curve; the fingers are longer and narrower than the mudflat fiddler; the merus (4th segment from distal end) of the 2nd walking leg is more slender, its dorsal edge straight; ridge on major palm is relatively low, center of palm clearly tubercled, tubercles on palm ridge continue around around carpal cavity to upper side of palm, The red-jointed fidder has red color in the joints of major claw and has no pile of hairs on the dorsal margin of its walking legs; The spined fiddler has straight anterio-lateral margins in its carapace. Other fiddlers may have no tubercled ridge on its inner palm of the major claw.
Bay, muddy bottoms, above the intertidal zone
Maximum Size
2.1 cm (1 in)
Other Common Names
Previous Scientific Names