I actually thought it was a very common hitchhiker. I have several different oysters, and several different clams in my tank. I can tell you 100% sure it's not a G. Maxima. I'll take some pics of the different oysters and clams I have when I get back. I'm on the road heading to Indianapolis. I have a wife, going to spend the weekend at her sisters, fun, fun. I'm taking my kayak and fishing pole and a 25.00 gift certificate to Premium Aquatics. That should get me out for a little. I'm rather certain it is a Comb Oyster, which exact species I'm not sure of. When I was a fisherman I'd see those stuck on clams and oysters all the time.