What has the worlds largest shell?

Answer 1

The largest shell is Tridacna gigas or the giant clam shell. There is also a pretty large shell in Australia called the Australlian Trumpet shell. And I am sure prehistoric shells were even larger then the ones of today.

Answer 2

The worlds largest conch shell is the horse conch. The shell is 606 millimeters wide and can be found on display at the Bailey-Matthews Shell Museum in Sanibel-Captiva, Florida.