Bob, No question about it that the pattern and coloration is that of a colored TD maxima, the only thing that is throwing me off here is the way the mantle 'flaps' open and the shell. It appears to be a BIG clam. I am not at all 100% convinced it's a maxigas. I wish Dustin or Dave would throw their two cents in on this as well.
P.S. Bob, any pics of yours? Sounds killer.