Biogenic guanine crystals are crucial for light perception in animals and photosynthetic microalgae. Their high refractive index and plate-like arrangement allow these crystals to participate in scattering, reflection, and image formation.
Interestingly, similar crystalline inclusions have been identified in phylogenetically distant photosynthetic microalgae. In Amphidinium carterae (Dinophyta), guanine crystals serve as long-term nitrogen stores and potentially contribute to light manipulation.