The particularly neat thing about this one is the pattern: a classic example of pattern-forming processes that have been successfully analysed mathematically. The mollusc, when it's alive, has a mantle whose edge contains cells that deposit pigment on the shell lip as it grows. These cells interact with their neighbours - they can switch on and switch off each others' pigment-making according to well-defined conditions - so the whole band of cells has a dynamically-changing linear pattern of pigment production; and as the shell grows, a record of that pattern is left behind.
|The Algorithmic Beauty of Sea Shells|
Whatever 'computational engine' drives the pattern changes on the shells is effectively a close analogue equivalent of the digital algorithmic device called a one-dimensional cellular automaton (you can play with an applet here). The outputs are very similar in appearance, and one celebrated example, Cymbiola innexa, displays Sierpinski triangles, a classic fractal pattern produced by many 1D cellular automata.
The rather peculiar aspect is - what function do these patterns serve? In many species of mollusc, the patterns aren't visible during life, as they're covered by a dull-coloured protective "periostracum", so camouflage or identification (the usual reasons for animal patterns) don't seem to apply. Do they have a function we don't yet know? Are they fossils of a past function that's better served by the tough periostracum? Or are they "spandrels" (the term borrowed from architecture by Gould and Lewontin for non-adaptive by-products of other adaptively evolved functions)?