Ophiocoma wendtii

The brittlestar Ophiocoma wendtii inhabits coral reefs from Bermuda to Brazil. It is known for its advanced compound eyes. Its arms are covered with calcite crystals. In addition to function as an armor and give structural support, the crystals makes up its unique visual systems, they minimize spherical aberration and can detect the direction of incoming light. The lenses work by filtering and focusing light on an underlying photoreceptor system. The only known animal to employ a similiar visual system, are the trilobites. Phototropic chromatophores changes O. wendtiis color from dark reddish during the day, to gray during the night. It does this to regulate how much light will reach the photoreceptors.