I think seashells are a great example of parametric objects in nature, so I was really interested in replicating similar structures in OpenScad.

This algorithm draws a a seashell as a series of cylinders rotating around a center. The algorithm takes as parameters a parameter proportional to the number of cylinders and a parameter for the width of each cylinder.

seashell(10,2);
module seashell(turns, spine) {
	for ( i = [0 : 0.2 : turns] )
	{
		rotate( i * 360/6, [100 * i, i, 0])
		difference () {
			cylinder(h=i, r=i*spine/10, center = true);
			cylinder(h=i/2, r=i*2, center = true);
		}
	}
}