Because you are posting in freshwater and said you got this crab at petsmart, I am thinking you got a terrestrial hermit crab. You aren't planning on putting this crab in a tank of water, are you? Because those hermit crabs they sell at pet smart live on land and will drown if you put them in an aquarium. There are aquatic hermit crabs, but the only ones I've ever seen for sale are marine hermit crabs that live in saltwater tanks. Can you post a picture of this crab?
Or are you trying to figure out the best way to add it to an existing population of terrestrial crabs? In that case I'm not really sure, I kept hermits occasionally as a kid but I never really got the hang of it. They didn't last long, because I didn't really know what I was doing.
