New clam!! But is this pinched mantle???

[Delphinus]

I'd actually vote on "wait a few days and see." It's not uncommon for clams to not fully expand the first few days. It's only fair, they're adjusting to new water

I don't have any good pictures of pinched mantle, but generally speaking the mantle is pinched all the way into the shell and it stays like this - ie. if it expands out the next day then it's not pinched mantle.

Or so I think anyhow. I'm not too "up" on pinched mantle so I could be off on this. But regardless, on the first or second day in the tank, I'd say it's too early to call at the moment.