Frae Wikipedia, the free beuk o knawledge
The shells o individuals within the bivalve mollusk species Donax variabilis shaw diverse coloration an patternin in thair phenoteeps.

A phenoteep (frae Greek phainein, meanin 'to show', an typos, meanin 'teep') is the composite o an organism's observable chairacteristics or traits, such as its morphology, development, biochemical or physiological properties, behaviour, an products o behaviour (sic as a bird's nest).