Biogenic guanine crystals are essential for light perception by animals and photosynthetic microalgae. High refractive index and plate-like arrangement allows these crystals be involved in scattering, reflection, and image formation.
Interestingly, similar crystalline inclusions have been found in phylogenetically distant photosynthetic microalgae. In Amphidinium carterae (Dinophyta), guanine crystals act as long-6term nitrogen stores and potentially play a role in light manipulation.