The Thallios

In the center of the cave, at the top of a pyramid, our heroes discover a sphere of orichalque floating on a lake. Attacked by thousands of giant crabs, they manage to take refuge inside. They are also surprised to find the emblem of the Shimazu but realize that it is just the shape of the key that they have recovered on his saber. By placing it on, they activate what turns out to be a ship with the shape of a nauplius sailing underwater! The Thallios!