Final answer:
Nautilus shells are from the class Cephalopoda, which also includes squids, octopuses, and cuttlefish. They use their coiled shells for protection and buoyancy.
Step-by-step explanation:
Nautilus shells belong to the class Cephalopoda, which is a large class of mollusks that also includes squids, octopuses, and cuttlefish. These marine creatures are known for their distinct shell shapes and sizes, and the nautilus is particularly noted for its beautifully coiled and chambered shell. The nautilus uses its shell not only for protection but also for buoyancy control while it traverses the depths of the ocean.