Starfish, or sea stars, possess eyes, though these structures are fundamentally different from what humans recognize as an eye. Their visual organs are simple and tailored to the specific needs of their underwater environment. This basic form of sight is a product of their unique anatomy, which lacks the complex systems found in other marine animals.
The Location and Appearance of Starfish Eyes
A starfish’s eyes are not on its central body; instead, a tiny eyespot is located at the very tip of each arm. This means a five-armed starfish has five eyes, while a species with 40 arms has 40 distinct eyespots. These visual organs are small, sometimes only half a millimeter wide, and can appear as a red or black dot. They are positioned at the end of a terminal tube foot, which is part of the groove on the underside of each arm that the animal uses for movement.
Each of these eyespots is a compound eye, a structure composed of several individual light-detecting units called ommatidia. An ocellus, or eyespot, is made up of a few hundred of these units. Unlike the more complex compound eyes of an insect, these simple versions lack a lens to focus light. This structural simplicity impacts the visual information the starfish can gather from its surroundings.
How Starfish Actually See
A starfish’s vision has extremely low resolution. Because their eyes lack a lens and have a limited number of light-collecting cells, they see a blurry, pixelated version of the world. They are unable to perceive fine details and are colorblind, only distinguishing between light and dark. Their visual system is also very slow, making it impossible to see fast-moving objects.
This form of sight is tuned to perceive large, stationary objects rather than dynamic ones. Their eyes are most sensitive to blue light, which means the surrounding water appears light to them, while large, dark structures like a reef stand out in sharp contrast. The image they perceive would be akin to a photograph taken with a very slow shutter speed, where moving elements become a blur, but static structures remain visible. This capability is sufficient for the animal’s needs.
The Purpose of Starfish Vision
This limited vision serves the purpose of navigation and survival. Starfish primarily use chemical cues to locate food and mates, but their eyesight helps them stay within their habitat. A starfish that has drifted from a large structure, like its home coral reef, can use its vision to find its way back.
By detecting the large, dark shape of the reef against the lighter open water, the starfish can orient itself and move toward shelter. This prevents the slow-moving creature from straying into open, sandy areas where it would be more exposed to predators. Their sight is perfectly adapted for their slow-paced existence and the specific navigational challenges they face.