The nautilus has many symbolic meanings. As the mollusk grows, its body moves forward into the new larger chamber and produces a wall to seal off the older chambers. The empty chambers are used to regulate buoyancy. A cross-section of the shell of the Nautilus will show the cycles of its growth as a series of chambers arranged in a precise Golden Mean spiral.
For myself, the nautilus is a metaphor of spiritual growth during the transitions of life. Passing through time and the chambers or doors perception that keep us growing and changing.
Oliver Holmes wrote, in a poem entitled The Chambered Nautilus, "Build thee more stately mansions, O my soul….Let each new temple, nobler than the last, Shut thee from heaven with a dome more vast, Till thou at length art free, Leaving thine outgrown shell by life's unresting sea!"