When a tiny parasite enters an oyster's shell, mantle cells cover it with nacre until this is formed
This sac secretes nacre to cover the irritant and, over time, the 
growing... [DOC] [TLE] ZACK'S ROCKS & MINERALS - Newsletter - Sample Issue [PAR] In this issue we will cover: The Birthstones of June (Alexandrite, Moonstone, and 
... Oysters and other shell-forming mollusks make a special substance, called ... 
shell or a tiny parasite, enters the body of the mollusk, the mantle cells begin to 
work.