A sea star belongs to the class Asteroidea. These creatures are famous for their radial symmetry and ability to regenerate lost limbs, leading to the question: do they possess the sense of sight? The answer is yes; sea stars have eyes, though they are vastly different from the complex camera-like eyes found in humans or other vertebrates. Their visual organs are simple light-sensing structures that provide a basic awareness of their surrounding environment.
Anatomy and Location
Starfish eyes are positioned at the end of each arm, or ray, not on the central disk. Most species have a simple compound eye at the tip of every limb, meaning a typical five-armed sea star possesses five eyes. These eyes are small and often overlooked, appearing only as a tiny red or black spot.
The visual structure is a compound eye, similar to those found in arthropods, but lacking the optics for sharp focus. Each eye is composed of numerous light-sensitive units called ommatidia. When moving, the sea star curls the tip of its arms upward, raising the eye spot off the substrate to gain a better view. This positioning provides the animal with a relatively wide, low-resolution view of its surroundings.
How Starfish Perceive Their Environment
Starfish visual perception is fundamentally different from a human’s, characterized by extremely low spatial resolution. Their vision is estimated to be approximately 500 times less acute than human eyesight, presenting the world as a collection of large, blurry pixels. This simple visual system does not allow them to see fine details or small objects.
The eyes are color-blind, perceiving the world only in shades of light and dark. Their photoreceptors are maximally sensitive to light around the 450-nanometer wavelength, which is the blue-green light that penetrates deepest in clear ocean water. This specialization allows them to optimize the detection of contrast, specifically the silhouette of a dark object against the bright backdrop of the open ocean.
The visual system also has low temporal resolution, meaning it is very slow, making them essentially blind to fast-moving objects. This slowness is suited to their deliberate movement, allowing them to focus on stationary objects. For example, the blue sea star (Linckia laevigata) uses this low-resolution image formation to detect large structures like a coral reef from at least one meter away. The eyes maximize contrast for navigation by making the open water appear bright while the reef registers as a large, dark mass.
Vision’s Role in Starfish Behavior
The limited but functional vision of the starfish plays a direct role in large-scale navigation and habitat maintenance. Experiments show that vision is primarily used to orient the animal back toward its preferred environment after being displaced. A sea star without functional eyes moves in random directions, but one with intact eyes successfully navigates back to the nearby reef structure.
This visually guided behavior is about selecting and maintaining a safe habitat, not finding food or mates, which are governed by chemoreception. The ability to distinguish the large, dark silhouette of a coral reef from the bright, open sandy bottom allows the sea star to avoid wandering into exposed, predator-vulnerable areas. Their slow visual processing is matched to their slow walking speed, measured in centimeters per minute.
The sea star’s visual awareness allows it to make broad directional decisions, such as realizing it is moving away from the safety of its habitat. By sensing the position of the reef structure, the animal can adjust its trajectory to remain in areas where food and shelter are abundant. This specialized vision is a tool for survival, ensuring the sea star stays within a life-sustaining environment.