Morphological variations were observed in the
megalopae; i.e., some larvae retained a dorsal spine or furcae on their telsons, which are zoeal morphological
features. The larval survival rates from the first-stage zoeae to the juvenile crabs and from the fourth-stage
zoeae to themegalopae decreased significantlywith increasing zoeal features in themegalopae,whereas survival
was not affected by the megalopal morphological features observed in the fourth-stage zoeae or any of the
culture factors. The carapace length of the fourth-stage zoeae decreased significantly with later hatching date
and increasing water temperature. The carapace length was the only factor that correlated positively with the
survival rate from the megalopae to the juvenile crabs, which suggests that nutrient accumulation during the
zoeal stages affects survival after the megalopal stage. Our study identified a relationship between the presence
of immature megalopae that retained zoeal morphological features and mass larval mortality from the last-stage
zoeae to the megalopae, which provides new insights into the causes of mass larval mortality in a brachyuran
crab.