Nudibranch color diversity shares a common physical basis in guanine photonic structure ‘pixels’

This coloration is typically a form of aposematism, warning predators against toxic compounds sequestered from their prey and weaponized as a form of defense. Although many of the hues in nudibranchs were thought to be of pigmentary origin, here we show, using a combination of white light and Raman micro-spectroscopy, that hierarchically organized micron-scale guanine multilayer structures are responsible for many of these colors.

Such architectures are widespread across the dorid and aeolid groups and are responsible for a striking array of angular-independent structural colors. By using cryo-FIB tomography, we were able to access the complex 3D organization of the guanine nano-platelets responsible for the strong blue coloration of Chromodoris annae. We propose that the multilayer organization of guanine platelets with varying orientations across the tissue and their micron-scale size offers a particularly effective strategy for producing diverse optical effects.