Department of Integrative Biology

Adults of the global invaders. Carcinus maenas and C. aestuarii, can generally be distinguished in the field by three diagnostic characteristics: the shape of the copulatory appendages (pleopods) in the male, the shape of the frontal area between the eyes, and the carapace width to length ratio. The pleopods of male C. maencas are crescent-shaped and curve outward with the center of the crescents touching; those of C. aestuarii are straight and parallel to one another. The frontal a-rea of C. maenas does not protrude and is bordered by three scalloped-shaped lobes with distinct bumps. The frontal area of C. aestuarii is flat without distinct bumps and protrudes beyond the eyes. The carapace width to length ratio of adult crabs is typically >1.29 for C. maenas and