The South American mud crab Panopeus austrobesus was described only recently (Williams, 1983) as one of six distinct species that formerly had been considered local forms of P. herbstii s.l. Milne-Edwards 1834. The larval development in this group of closely related species has been described only in P. herbstii s.s. (or, possibly, P. obesus?) from Beaufort, North Carolina. In the present study, larvae of Brazilian P. austrobesus were reared in the laboratory from hatching to metamorphosis. Development consists of a non-feeding prezoea, four zoea, and one megalopa stage. Duration of each of the zoea stages at 25 °C is 4 to 6 d, and in the megalopa stage about 10 d, i.e. total larval development duration lasts ca. one month. The morphology of the larvae is described and compared with that of larvae of P. herbstii s.s. (?) and of the three Panopeus species, P. americanus, P. occidentalis, and P. bermudensis, that occur on the Brazilian coast and for which descriptions have recently become available. Comparison of characters considered plesiomorphic reveals that each larval stage can be clearly distinguished from the corresponding stage in P. herbstii s.s. (?) and in the other species. Surprisingly, some morphological characters of P. austrobesus larvae show similarity more to P. bermudensis rather than to P. herbstii (?) from Beaufort. Possible relationships among these species are discussed, and an identification key is given for the larval stages of the above mentioned Brazilian Panopeus species.