1. Poseidon's Palace: When Percy, Tyson, and Annabeth arrive at Poseidon's palace, they find the palace adorned with pearls. Amphitrite, Poseidon's wife, wears a necklace made of large, glowing pearls.
2. Polyphemus' Lair: When Percy and Tyson encounter the giant Polyphemus, they notice a pile of treasures in his cave, including a heap of pearls.
3. The Garden of the Hesperides: The Garden of the Hesperides, guarded by the dragon Ladon, is where the Golden Apples are kept. Percy discovers that the tree with the Golden Apples also bears giant pearls.
4. The Quest for the Golden Fleece: The Golden Fleece, which Percy and his friends seek to retrieve, is guarded by a number of monsters, including the Sirens. The Sirens lure people with their enchanting songs and turn them into mindless servants, sometimes using pearls as bait.
5. Scylla and Charybdis: When navigating between Scylla and Charybdis, the two dangerous sea monsters, Percy notices that the path is marked by glowing pearls to guide ships safely through the narrow passage.
6. Percy and Annabeth's Relationship: In the book, there's a subplot involving a pearl necklace exchanged between Percy and Annabeth as a symbol of their friendship and growing feelings for each other.
Throughout The Sea of Monsters, pearls are associated with wealth, beauty, and magical properties, and they play a symbolic and significant role in various parts of the story.