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Simple Eyes
Less complex animals, such as earthworms and seastars (starfish), don't have brains or the kinds of eyes that can see images. Instead, they have light-sensitive cells or cell clusters called "simple eyes." Simple eyes detect light, dark, and sometimes motion.
 There are two types of simple eyes: eyespots and eyecups. Eyespots are light-sensitive cells distributed over an animal's body. Eyecups are clusters of light-sensitive cells forming cup-shaped depressions on an animal's body.
Earthworms have eyespots. When its eyespots detect light, it's stimulated to move. Seastars have eyecups. The eyecups are located at the ends of their arms. This arrangement allows the seastar to detect changes in light from several directions at once -- a useful ability in a predator-filled environment such as the ocean.
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