(nô′tə·ləs) noun plural ·lus·es or ·li (-lī)
1. Any of a family of cephalopod mollusks containing a single surviving genus (Nautilus) found in southern seas and having a natant spiral shell containing a series of empty chambers lined with mother-of-pearl that are successively secreted and then sealed off as the animal outgrows them.
2. The paper nautilus. [<L <Gk. nautilos, sailor]
CHAMBERED NAUTILUS
Cross–section
(The shell up to 10 inches across)

The first atomic-powered submarine, launched by the U.S. Navy: made the first undersea crossing of the North Pole on August 3, 1958.