taken from a walkthrough on Gamefaqs, which is what you should all read before asking here.
quote:
Look around at the scenery...it's quite nice. Swim underwater and enter a cavern near the shore. When you come out on the other side, walk to an open room. Shoot the switch on the other side of the room to free Carmen the whale. Go back to the room and you find a walking shell. Ride it through the only exit and hit B to accelerate before you hit the gap. You sail over it into the X-door on the other side, which has a cage inside the room. Make your way back to the open ocean.
Find Carmen the whale and swim through the air bubbles he leaves behind. In the next area, do the same, except go faster, or the piranhas might get your air. When you see a ship, diverge from the path. If you want a crystal, go to the cavern left of the ship. When you reach the surface from this place, jump on the platform and bounce up to the *THIRD CRYSTAL*.
Return to the area where you left Carmen and go straight to the ship. Swim up into a new area. Start this area by climbing to the top of the ship. Find a purple lum and use it to swing to the top compartment(I don't know my ship parts...), in which you find a cage. Jump your way over to the water slide and grab the lums on your way to the land. Climb to the cave with the monkey-pirate in it and free the Teensie. Go to the exit above.