Well, I have never purchased a clam online, but I did have a rather unique "clam shipping" experience this past week. I was in Ft. Lauderdale, FL this week on business and found two really nice green T.Crocea clams at <a href=http://www.coralreeffarm.com/corals.php>Coral Reef Farm Exotics</a>, which was only about 2 miles from the airport..... so I decided I would try my chances with the TSA (airport security) and carry them onboard the plane with me. David @ CRF did a wonderful job packing them, only to have airport security force me to pour out almost all of the water in the bags!!!. The clams are about 2 inches in length, and the water just barely covered them in the bags. I thought for sure that they were goners. All in all, they spent roughly 6 hours in the bags (the temp of the water got pretty cool on the flight). I got home, acclimated them for about 20 min (eeeek) and in they went. This was Thursday night and as of today, both are doing well. I wont challenge the TSA again!
So... I would have to say that clams ship pretty well. Healthy livestock certainly make it easier.