Simple eye

A light-sensitive organ in an invertebrate that detects light intensity or direction, typically without forming a detailed image.

Photoreceptor cell: A sensory cell that converts absorbed light into electrical or chemical signals. Photoreceptor cells provide the light-sensitive machinery in simple eyes.
Ocellus: A simple photoreceptive organ, often a small cup or lens-bearing spot, that detects light. Ocelli are a common form of simple eye in insects and other invertebrates.
Compound eye: An eye made of many repeating visual units, each with its own lens and photoreceptor array. Its many ommatidia contrast with the simpler organization of a typical simple eye.
Photoreceptor: A cell or sensory structure that responds to light by producing a biological signal. Simple eyes depend on photoreceptors, whether organized into a discrete organ or not.
Evolution of the eye: The evolutionary history and diversification of light-sensing organs across animals. Simple eyes are widespread forms in the evolutionary diversification of animal light sensing.
Rhabdom: A light-sensitive structure formed by densely packed microvilli in photoreceptor cells. In many invertebrate eyes, rhabdoms capture light and support directional sensitivity.
Nauplius eye: A median larval eye found in many crustaceans, typically with a few photoreceptive cups. This compact eye gives crustacean larvae a distinct example of simple visual organization.
Camera eye: An eye that forms an image by focusing light onto a photosensitive surface. It contrasts with simple eyes that detect light without resolving detailed images.
Pigment cell: A cell containing pigment that absorbs or blocks light. Pigment cells can shade photoreceptors, helping simple eyes distinguish light direction.
Bilateral symmetry: A body plan in which left and right sides are approximate mirror images. Directional sensory organs often evolve near the front of bilaterally symmetric animals.

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