Yes, it turns: experimental evidence of pearl rotation during its formation
Cultured pearls are human creations formed by inserting a nucleus and a small piece of mantle tissue into a living shelled mollusc, usually a pearl oyster. Although many pearl observations intuitively suggest a possible rotation of the nucleated pearl inside the oyster, no experimental demonstration of such a movement has ever been done. This can be explained by the difficulty of observation of such a phenomenon in the tissues of a living animal. To investigate this question of pearl rotation, a magnetometer system was specifically engineered to register magnetic field variations with magnetic sensors from movements of a magnetic nucleus inserted in the pearl oyster. We demonstrated that a continuous movement of the nucleus inside the oyster starts after a minimum of 40 days post-grafting and continues until the pearl harvest. We measured a mean angular speed of 1.27° min−1 calculated for four different oysters. Rotation variability was observed among oysters and may be correlated to pearl shape and defects. Nature's ability to generate so amazingly complex structures like a pearl has delivered one of its secrets.
Gueguen Yannick, Czorlich Yann, Mastail Max, Le Tohic Bruno, Defay Didier, Lyonnard Pierre, Marigliano Damien, Gauthier Jean-Pierre, Bari Hubert, Lo Cedrik, Chabrier Sebastien, Le Moullac Gilles (2015). Yes, it turns: experimental evidence of pearl rotation during its formation. Royal Society Open Science. 2 (7). 150144. https://doi.org/10.1098/rsos.150144, https://archimer.ifremer.fr/doc/00275/38598/