Ok here are some pic's of my old Giga's, I had it a year and then sold it cause it was outgrowing my tank. I bought it at 1.5" and sold it a year later at 7".
Here it is right before I sold it, sorry about the pic quality.
Here it was at about 4" notice the new shell growth.
And at about 1.5" when I brought it home.
Funny story, one day I was watching the tank and I noticed the clam kind of hopping slowly across the bottom of the tank on it's side. Upon closer inspection I noticed the clam had attached to one of my conch's, the conch was dragging it along for a ride.