I personally love clams and am making funds for a nano clam-only tank. My favorites are crocea's and maxima's with some dersa's. And to keep them alive just provide a mature tank (IMO 6 months and up), really good water parameters, good and stable (stability is the key here) calcium and alkalinity levels, strong lighting, and a friendly environment (so they don't get eaten or harassed by other mates in the tank)