If it doesnt show full mantle extension within the first few days I think you have a problem. I hope you don't have any other clams in your tank. You might infect them with whatever the little max has.
All clam keepers should read this thread(and the links posted)
http://reefcentral.com/forums/showth...antle+pinching
Your clam looks like it is stressed but it is not a goner if you do something about it.
FWIW I fed my clams for almost 2 years using the bowl feed method. I haven't fed my clams directly lately(they grow fast enough as it is) but if I do pick up some smaller clams I will feed them via a 2-liter bottle attached to airline tubing seen here
http://reefcentral.com/forums/showth...c&pagenumber=2
Either way works well, feed them babies!