 The marine hatchetfish is extremely flattened laterally , leaving the body just millimetres thick , and the body is so silvery as to resemble aluminium foil . The mirrors consist of microscopic structures similar to those used to provide structural coloration : stacks of between 5 and 10 crystals of guanine spaced about ¼ of a wavelength apart to interfere constructively and achieve nearly 100 per cent reflection . In the deep waters that the hatchetfish lives in , only blue light with a wavelength of 500 nanometres percolates down and needs to be reflected , so mirrors 125 nanometres apart provide good camouflage . 
