Is it normal for my emerald crab that i bought a few months ago to not have molted a single time yet? compared to my shrimps and hermit crabs which molt atleast every month or so. longer for my hermits but shrimps pretty often.
Yes. They only live a few years and likely they won't molt in an obvious spot even if they were. I had two crabs that didn't molt for months. Anecdotally, iodine seems to influence molting in shrimps and crabs, and the amount they're eating and converting to mass will also influence their molt rate. As long as they're healthy, I wouldn't worry too much. Crustaceans continually grow, just at various rates depending on multiple factors.