Pearl white chest without key or lid. Inside of which golden treasure is hid. What am I?

“A coconut”

While a coconut has a hard shell and is white inside, it does not fit the description of having a 'golden treasure' inside, as it contains water and coconut meat rather than something golden.

“A clam”

A clam does have a shell and can contain a pearl, but it doesn't match the description of being 'pearl white' and typically does not have a 'golden treasure' inside.

“A treasure chest”

A treasure chest typically has a key or lid, which contradicts the riddle's clue of being 'without key or lid', making it an incorrect guess.