the platelets is on the same order as the wavelength of visible light the plates lead to structural coloration and iridescence through the physical phenomenon described as thin-film optics. The most common color produced in this fashion is blue, such as in the Morpho butterflies. Some types of spiders also have scales. Spider scales are flattened setae that overlay the surface of the cuticle. They come in a wide variety of shapes, sizes, and colors. At least 13 different spider families are known to possess cuticular scales, although they have only been well described for jumping spiders (Salticidae) and lynx spiders (Oxyopidae). See also Scale (insect anatomy) Armour (anatomy) Psoriasis: a long-lasting autoimmune disease characterized by patches of thin pieces of hard skin like scale. References Further reading Animal anatomy Marine biology Integumentary system