A found a pearl in a king crab leg last month (Chistmas dinner '08). While I fiddled with it it separated into two pieces. You could clearly see the stone in the center that caused the irritation. The pearl substance was in the process of coating it from both sides and had almost reached the point where the stone was fully covered.
I think it would be very thrilling to find a "pearl" in a crab. Even if these pearls aren't technically pearls, they have similarities and I appreciate you sharing your story here.