The tip of each arm of a sea star is equipped with a small red-pigmented eyespot containing about 100 light sensitive cells in a tiny cup. The sea star in this photo is the giant sunflower star, with 21 arms, so this animal has 21 different eyes. Unlike the eyes of vertebrates, insects and octopus, the eye does not form an image. Instead, it allows the animal to distinguish between light and dark.
Most sea stars are positively phototactic - they move towards light.
While the ability to distinguish light and dark may help it find better habitat, most sea star's sense their environment primarily with a kind of smell - chemical reception. If the sea star detects a chemical signal from a prey animal, it moves in the direction of the arm receiving the strongest signal. In this way, it can relatively quickly find a prey animal. This material may be copied for use in student classroom projects and reports. Limited permission is provided for teachers and educational web sites.