The Atlantic mud crab, Panopeus herbstii, is one of many species of mud crabs belonging to the family Xanthidae. Crabs included in Panopeus and related genera have five teeth lining the outside of the carapace on each side, the first two mostly fused (Gosner 1978).The fingers, or top and bottom portions of the closable claw, are usually black to brown in most species; whereas, the interior portion at the base of the claw, called the palm, is usually pale. The claws are distinctly unequal in size, and the body is brownish. The carapace of P. herbstii is brownish green and slightly granular in texture, with sharp 2nd, 3rd, and 4th marginal teeth on either side (Kaplan 1988, Voss 1980). The appendages bearing the claws, called chelipeds, are darker and often spotted. Both fingers on each claw are black, and the color of the lower finger often extends up the palm. An enlarged, white tooth is present at the base of the upper finger on the larger claw (eg. Ruppert & Fox 1988). The 3rd maxilliped, or feeding appendage, is marked with a red spot in males, sometimes in females (Gosner 1978). All walking legs are hairy and slender (Voss 1980).