You might find a pearl. Needs to be a big oyster, the photo is of the 00 size oysters, which is usually the largest size offered from the sellers at the markets. Bigger ones exist, but they would really be too big. 00 is a bit large, as you can see. They were good, difficult to open as they really fight back. I think 1 and 2 are good eating sizes.
Yes, there was a pearl. Not a big pearl and probably not a good pearl, as these are not pearl oysters. But my pearl nevertheless.