Megalobrachium poeyi (Crustacea, Decapoda, Porcellanidae): Comparison between Larval Development in Atlantic and Pacific Specimens Reared in the Laboratory'

THE P ORCEL LANID CRAB GENUS Megalobrachium, which contains 11 known species, is confined to the new world. M egalobrachium poeyi (Guerin-Meneville, 1855). is, at present, the only member of this mainly tropical, intertidal genus with forms on both sides of the Panamanian isthmus. Originally considered an Atlantic species, it was apparently not collected on the Pacific coast unt il 1926 (see Boone, 1931, p. 150; Haig, 1960, p. 339) and is still considered uncommon on that side of the continent (Haig, 1960, p. 215) with a range restricted to Panama and Costa Rica (Haig, 1968, p. 72). The male and female crabs collected on the Pacific coast and reported herein bring the known total of Pacific specimens to 15. Megalobrachium poeyi has no known analogous or geminate species, although several other species have closely related forms on each side of Panama (e.g., M. erosum and M . mortenseni, see Haig, 1962, p. 191). Because fossils are lacking, it is not known from which side of the continent M . poeyi originally came, and whether the species was an early or recent migrant. It is widely distributed throughout the Caribbean Sea. Its apparent