What is a "simple eye"?

A simple eye refers to a photoreceptor organ found in many invertebrates, such as insects, crustaceans, and mollusks. They are composed of a single lens and a few photoreceptor cells, which detect the direction and intensity of light. Unlike complex eyes, which have multiple lenses and can form images, simple eyes can only detect the presence or absence of light. Simple eyes can be found on different parts of the body, depending on the species, and may serve various functions, such as navigation, predator avoidance, and regulation of circadian rhythms. Overall, simple eyes provide a basic level of visual perception, allowing animals to respond to changes in light intensity and direction in their environment.