Shell patterns
Seashells and snail shells often exhibit interesting patterns. The growth algorithm of many shells leads to spectacular expanding helical shapes. Here is one whose interior has been exposed to view by natural polishing. A small pebble has been trapped by the shell.
As a shell grows, the pigment on the shell can evolve patterns that are surprizing similar to those seen in simple one dimensional cellular automata. The time history of the growing edge is recorded in the color pattern on this shell.
The Experimental Nonlinear Physics Group, Dept. of Physics, University of Toronto,