natural pearl from the Lima vulgaris bivalve ?

[water]

Hi everybody,
I am presented with a white, 7mm, button shape pearl (see attached photo) supposedly coming from the Lima vulgaris bivalve, and displaying a pseudo "flamme structure". Has anybody ever come across such a natural pearl ?

Furthemore, i was under the impression that the "flamme stucture" could only be found in univalves such as the Conch or the Melo. Does anybody know wether such structures are indeed found in pearls found in bivavlves, and if this is the case, which ones ?

Many thanks  <img src="images/smiley/jap.gif" alt="" border="0" />
Water
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