If it is a pearl, and not carved out of shell, it is much more likely to have come from Tridacna gigas, but this is highly unlikely. Anything of size is usually attached to the shell and not round. Honestly, what you are showing looks like it was carved from shell. Try shining a single spotlight above it to look for a "ring of fire" flame pattern that might indicate that it is a pearl.
The first photo in your post looks like an operculum and not a pearl at all. Can you tell me what the post number was?
I recall the discussion. Everyone agreed the specimen was gastropod operculum.
As for the other images, Blaire is correct that it's carved shell. All pearls present with closed, fully enveloped concentric lines radiating outward from the nucleus, but this piece has visibly bisected lines, meaning it was cut from a large, thick shell. The color and structure is consistent with Tridacna gigas.