Little wonder then that natural selection favored jumping spider ancestors with better visual systems - in this case with multiple sets of eyes. Jumping spiders use their 8 eyes to gauge distance and detect moving prey. Four long tubular eyes on the face form very sharp images but have a narrow field of view. Jumping spiders also have four eyes on the top of the head - 2 toward the back and 2 toward the front. These eyes effectively broaden the spider's field of view, acting mostly as motion detectors and do not form sharp images.
Some types of spiders use auxiliary eyes to detect polarized light.
This helps in navigation and guides them back to their nest after a day of hunting. It is equipped with a loose network of nerve cells called a nerve net, and it lacks a major concentration of nerve cells that could be called a brain. To observe the light in its environment it has simple eyespots at the base of each tentacle, each shielded by a patch of bright red pigment. The shield casts a shadow on the eyespot which helps the animal to determine its orientation and the surrounding light conditions. Poke around any rocky seashore and you are likely to see a sea star, a member of the Phylum Echinodermata, the spiny-skinned animals.