Iridophore

An iridophore is a type of chromatophore, a pigment-containing or light-reflecting cell in the skin of some vertebrates. Iridophores contain guanine-based platelets that form organized reflectors, producing structural coloration. The reflected color depends on platelet thickness and spacing and can appear blue, green, or silver.

Because the color arises from light interference rather than pigments, iridophore-based coloration is often highly iridescent and can shift with viewing angle. Iridophores are especially common in many fish, some amphibians, and certain reptiles. They typically lie in the dermis beneath pigment-containing chromatophores such as xanthophores and melanophores, and may work in concert with these cells to create complex patterns.

The brightness and hue of iridophore reflections can be modulated by physiological factors, including neural and hormonal signals, and by the rearrangement or shading of surrounding chromatophores, enabling rapid color changes in some species. In development, iridophores originate from neural crest cells during embryogenesis. The exact arrangement and density of iridophores contribute to species- and individual-specific coloration, including mimicry, camouflage, and signaling.

Related pigment cells include leucophores, which can also reflect light via guanine but are typically described separately as white reflectors.