The mottled shore crab, Pachygrapsus transversus, is a small intertidal crab belonging to the family Grapsidae. Members of this family are characterized by squarish carapaces with few spines (Voss 1980). The color of the carapace in P. transversus is dark green to black, and the surface is covered with oblique lines of fine tubercles or bumps (Abele et al. 1986, Ruppert & Fox 1988, Voss 1980). The sides converge toward the posterior end to form a trapezoidal shape, and the area between the eyes is slightly curved and bears no teeth. The claws are brownish to pink or cream, with a smooth upper surface on the movable finger. Teeth are present on the hind margins of the largest joints on the legs. Unlike many crabs, there is no sexual dimorphism in claw size, and the total body size of males is larger than females (Abele et al. 1986).