The Black Pearl Necklace is a collar accessory in Nintendogs + Cats. It is a chain-link necklace with five black pearls on the front with the middle being the largest, the two on either side of it being smaller, and the two on the end being the smallest. It can be bought from the Seaside BARC for $200 after being unlocked by 5,400 Owner Points or by playing for 20 days consecutively. The Black Pearl Necklace also has a white counterpart.
3DS: "Beautiful black pearls line this striking and refined necklace."