The Crystal Trident is an item found within the Sunken Ship in the bottom of the ocean kingdom, Atlantica. It appears to be a small blue replica of King Triton's own Trident without a handle. It is supposed to have the power to reveal Atlantica's Keyhole. Once Sora obtains it, he brings it to Ariel's Grotto, but King Triton destroyed it before they had the chance to use it.
It was restored after the defeat of Ursula, when Triton used the power of his trident to reveal the world's Keyhole.