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. Each of the sea star's tube feet is covered with chemo-sensory cells - as many as 50,000 per square millimeter. 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. By the way, the giant sunflower star of the Pacific coast (Pycnapodia helianthoides) is among the world's fastest echinoderms, moving across the substrate at speeds up to 5 meters per minute!