Mosaic floor from Tunisia, showing Medusa in the center. Mosaic fragment from Antakya Archeological Museum, Turkey, 3rd century A.D. Patterns of both pieces are based on the shape of the ‘scallop’ and the design was widespread in Roman and Byzantine mosaics. Scallop, or shell, or scale principle of space division comes entirely from nature. Fish scales, pine comb, peacock tale are just a few examples of that.
Symbolism of the ‘scallop’ goes back for centuries. Most likely it was associated with Aphrodite worship. Byzantine art inherited Greco-Roman shapes and started to imply them in Christian context.
In Islam the shell is associated with the pearl which is one of the Islamic symbols of the Divine Word. Mihrab niche is often ends up with a scallop shape and it is not a mere decoration. As Mihrab shows a direction of Mecca and symbolizes a Divine enlightenment through the Divine Word represented by Qur’an.
In Japan the pattern is called nami – wave. Although it is not a scallop but it still associated with the sea. The scallop-shell-nami-scale patterns always give a wavy movement. Pattern doesn’t look static. The geometry of scallop is very simple. It is basically a pattern of one shape repeated. Simple designs always work.
Maybe because of its long and great history the scallop design was widely replicated in modern ( since 18th century) European design. There are lots of variation of it everywhere.