It is a jellyfish that is white and is much larger than a normal jellyfish.
Role in game
The giant white jellyfish can be seen in the level Jellyfish Fields in the second area of "Jellyfish Clams," which the player accesses by entering a cave on a hill in the first area of Jellyfish Clams. If the player follows the right-hand side of the canyon wall, they will eventually find the jellyfish. Then, if the player jumps on its cap, it will rise out of its "bed" and take SpongeBob for a ride. Avoid falling into its bed; if done so, it will automatically kill SpongeBob.
When riding, the objective is to avoid falling off the cap. The jellyfish will go under a series of narrow bridges made of rock and make a series of tight twists and turns (the ride will get increasingly harder as the player goes through it). As the ride progresses, changing the camera angle will become more of a necessity. If SpongeBob stays on the cap while it is going under a bridge, he will be pushed off of the cap, due to the small amount of space between the bridge and the cap. In that case, SpongeBob will need to jump over the bridge and land back on the cap of the jellyfish. If he falls off of the cap, he will need to get back on the cap in ten or fewer seconds. If SpongeBob does not succeed in doing so, he will have to start all over again. If he does succeed in staying on for approximately three minutes, the player will be rewarded with a 'B' letter tile.
About two-thirds of the way through, the Giant White Jellyfish makes a slow turn around a sleeping giant clam sitting on a raised section of a rock. If the player has enough time, they can jump on the clam, making it spring its mouth open, hurling the player up in the air, where an 'E' letter tile is floating. The player can grab it and then land back on the cap of the jellyfish before ten seconds is up.