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Although the crab Hymenosoma orbiculare appears to complete its entire life cycle within estuaries, the salinity and temperature requirements for its successful larval development are not known. The present study therefore evaluated larval response to salinity and temperature in combination. Larvae were reared individually in factorial combinations of salinity (14, 21, 28, 42 and 49 ppt) and temperature (12, 16, 20, 24, 28 and 32°C). Both parameters influenced the probability of survival for any individual larva. Highest survival occurred at salinities of between 21-35ppt for the Zoea 1 and 2 and of between 28-35ppt for the Zoea 3, with optimum temperature ranges narrowing substantially from Zoea 1 through Zoea 2 to Zoea 3. Temperature exerted a similar influence on development rate at all rearing salinities within each zoeal stage. However, elevated salinity (42 ppt) delayed development. H. orbiculare larvae appear to be well adapted to tolerate salinities typical of the estuarine environment, but the range of salinities tolerated is narrower than expected, considering that the larvae have been recorded at salinities as low as 1ppt in the estuarine environment, and in freshwater in Lake Sibaya, a relict estuarine lake.