How long was the acclimation? A 2hr drive should be fine unless there were some very large and rapid temperature swings?
I've never heard of clams taking that long to acclimate. They can take a while to find a spot they're happy with but an acclimation should take about an hour or two depending on the differences. And once they're in a tank they're acclimatised, unless you're talking about light acclimation?
The way I see it is, see the inlet siphon how it's really widely open and the edges are in-turned? This is the clam gaping which is a very poor indication of health. The next very worrying sign is that the clam is open and tissue exposed like it should be but the difference is the edges of the mantle are retracted inside the shell. This is also another bad indication of health
I will be truly happy to hear that this clam makes it and thrives but given the signs I don't give it much chance I'm afraid.
Please have a read through this article, written by the Grand Father of clams himself, James Fatherree:
http://www.advancedaquarist.com/2009/3/aafeature1