Mussel pearl - blister? (New Zealand)

by Michelle Forrest
(Waikouaiti, Otago NZ)

We were walking the dog down the beach this evening when my daughter and I decided to try and find large mussel shells. She picked up a shell that still had both sides (only just attached) but was empty, so she pulled the 2 halves apart and washed the shells in the sea water. Lo & behold it looks like there is a decent sized pearl half embedded into the shell!

The shell itself is 11.5mm long from top to tip and the pearl is about 6-7 mm wide. It has other tiny wee bumps inside the shell also which look like the start of other pearls.
Can you tell me anything about it? I'm from the Dunedin, New Zealand area & assume its just a standard old mussel (?).
Any info would be greatly appreciated :-D