Basic Account, Created on 2 April 2005 (#6667796), Last updated on 14 March 2012 [Gift]
"When a mollusk is invaded by a parasite or is irritated by a foreign object which the animal cannot eject, a process known as encystation entombs the offending entity in successive, concentric layers of nacre. This process eventually forms what we call pearls and continues for as long as the mollusk lives."