Larvae and early juveniles of a mud crab, Eurytium limosum, originating from a brackish south Brazilian mangrove swamp were reared in the laboratory. Morphology of all larval (4 zoeae, 1 megalopa) and the first two juvenile stages was studied microscopically and described in detail. These results were compared with an available (but much less detailed) morphological description of larval E. limosum from the North Atlantic (KURATA et al. 1981), in order to find possibly existing geographical variation and to provide additional details. Conspicuous morphological differences were found in the spinulation of the antennal exopods (zoea II), in the setation of maxillipeds 1 and 2 (zoea III), and in setation of the carapace (zoea IV). Cultivation experiments were conducted at four different salinities (15, 20, 25, 32 S) and a constant temperature (25 °C). Conditions with polyhaline water (25 S) were optimum, resulting in maximum survival. Lower salinities (*20 S) and seawater (32 S) were also tolerated quite well by all four zoeal stages. In contrast, the megalopa showed a less euryhaline response, with clearly highest survival at 25 S. While salinity exerted in general strong effects on larval survi-val rate, development duration showed only exceptionally a conspicuous response: 15 S caused statistically significant delays in the zoea I and III stages, and the zoea II developed significantly faster at 25 S than in all other salinities tested. These results suggest that the larval development of E. limosum predominantly takes place in the outer polyhaline parts of estuaries.