Larvae of the South American mud crab species Hexapanopeus schmitti were reared in the laboratory from hatching to metamorphosis. Development consists of four zoeal stages and a megalopa. Duration of each of the zoeal stages at 25 degree C is 2-5 d, and in the megalopa 7-9 d, i.e. total larval development duration lasts approximately three weeks. The morphology of the larvae is described and compared with that of larvae of H. angustifrons, the only other species within the same genus for which a description of larval stages is available at present. The zoeae of H. schmitti differ from those of H. angustifrons mainly in the absence of lateral carapace spines and in the number of both internal and external lateral spines on the telson. The megalopa can be distinguished by the number of aesthetascs and setae on the antennule, the setation of the antennal flagellum, the mouth parts and maxillipeds, and by the presence of spines on the surface of the scaphognathite of the maxilla. ! The latter feature has not yet been observed in other xanthid species.