You may have luck with brine shrimp or other food you might use for feeding salwater fish.
They don't live underwater like most other crabs so I wouldn't keep them in a tank where they can't have a shore which is where they dig their tunnels.
I would think they probably have gills though since their burrows are underwater when the tide comes in.
They're not animals I've ever seen in an aquarium shop so your informational resources may be limited...I'd try searching the net though.
Good Luck --Kevin--
German Tour Guide: You vill find more on Germany's contributions to ze arts in ze pamphlets ve have provided.
Brian Griffin: Yeah, about your pamphlet... uh, I'm not seeing anything about German history between 1939 and 1945. There's just a big gap.