Simple eye in invertebrates

Simple eye without retina

A simple eye or ocellus (sometimes called a pigment pit) is a form of eye or an optical arrangement which has a single lens without the sort of elaborate retina that occurs in most vertebrates. These eyes are called "simple" to distinguish them from "compound eyes", which have multiple lenses; they are not necessarily simple in the sense of being uncomplicated or basic. The structure of an animal's eye is determined by the environment in which it lives, and the behavioural tasks it must fulfill to survive.

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