Greek iris (iridos) rainbow + kytos cell.

Iridocytes - large, oval-shaped cells, have no pigment grains, but contain guanine crystals, which cause the silvery coloration of fish.

Pigment cells in which the layers of protein plates, guanine crystals and cytoplasm alternate. Because of the different refractive indices of these layers, pigments interfere with light waves, and can reflect light from ultraviolet to far red. This is how bright and varied colors are produced - iridiocytes give luster to the covers of fish and mollusks. Fish can quickly change the ultrastructure of these cells to scatter or absorb light. The functions of these pigments are diverse: to protect against overheating, to help intraspecific communication, to serve as camouflage.