Pigment Patterns on Sea Shells — A Beautiful Case of Biological Pattern Formation

The patterns on shells of mollusks display an enormous diversity and are frequently of great beauty. Shells consist of calcified material. The animals can increase the size of their shells only by accretion of new material along a marginal zone, the growing edge of the shell. Therefore, the formation of these patterns proceeds in most species in a strictly linear manner. The second dimension is a protocol of what happens as function of time. The shell patterns resemble, so to say, a space-time plot. They provide an unique situation in which the complete history of a highly dynamic process is preserved. They are thus very convenient to study general properties of pattern forming systems. Models for these patterns will be discussed. By computer simulations, it will be demonstrated that even fine details in the pattern can be faithfully reproduced.