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A shell that displays the Fibonacci spiral. Fibonacci's sequence and phi are important mathematical concepts (especially in biology) in the same way Planck's constant is important to Quantum Mechanics.
Benoît Mandelbrot: Remembering The Father of Fractals
a metaphor of the human experience: "The main feature of the Nautilus is the large snail-like shell that is coiled upwards and lined with mother-of-pearl. The shell is subdivided into as many as 30 chambers. As the shell 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."
Nautilus Shell. The nautilus inhabit the deep slopes of coral reefs. The shell coloration keeps the animal cryptic in the water. When seen from above, the shell is darker in color and marked with irregular stripes, which helps it blend into the dark water below. The underside is almost completely white, making the animal indistinguishable from brighter waters near the surface. This mode of camouflage is named countershading. --Wikipedia