make a new account with a new email address, hotmail or gmail or something. best to do to get an answer from them quicker, it seems they've seen almost everything to do with clams
You don't see anything along the shell rim that might affect the mantle at all do you? Also is there a chance that something fell into the clam? Have a good look in the incurrent siphon, perhaps some sand or something got lodged in there and its doing its best to get it out or something? Just a thought. I don't know what else to suggest.