1. A structure found in some free-swimming unicellular algae and in plant reproductive cells that contains orange or red pigments (carotenoids) and is sensitive to light. It enables the cell to move in relation to a light source (see phototaxis).

2. A spot of pigment found in some lower animals, e.g. jellyfish.

3. An eyelike marking on the wings of certain insects, which is revealed in startle displays.