That looks to be a
tridcna maxima to me. You can tell by the way the shell growths are spaced on the shell, the mantle looks like it too but that's a harder one to judge but I'd definitely say t. maxima
Yeah, it'll take the little guy a few days to open to the full extent as it adjusts to it's new surroundings and home. Make sure you have a small rock underneath it so it can attach it's foot to it
It'll also make life easier for you if it's on a small rock and you have to move it around. A rock will also help protect the clams sensitive and unprotected foot
Strong light and lots of love that little fella will grow into the beauty that it is!!