“111. Some authorities state that groups of shells, like swarms of bees, have an especially large, old shell as their leader – one marvellously skillful at looking out for dangers – and that divers deliberately seek these shells, since, when they are caught, the rest wander aimlessly and are easily trapped in nets. Then they are heavily salted in earthenware pots; the salt eats away all the flesh, and the nuclei, as it were of their bodies, namely the individual pearls, sink to the bottom.”

(Pliny the Elder in Book IX (“Creatures of the Sea”) of Natural History; p. 136 in John Healy’s Natural History: A Selection.)