Sea stars are marine invertebrates known for their unique body plan. Despite lacking traditional sense organs like eyes or ears, they possess a sophisticated array of sensory capabilities. These senses allow them to navigate their environment, locate food, and avoid predators. Their sensory abilities differ significantly from more familiar animals, sparking interest in how these creatures interact with their underwater world.
Touch and Physical Sensations
Sea stars perceive their physical environment through touch, pressure, and surface texture. Their thousands of tube feet, covering the underside of each arm, are highly sensitive to these stimuli. These tube feet function for locomotion, allowing the sea star to glide across the seafloor, and enable them to grip surfaces and manipulate prey. When a tube foot encounters an object, it can retract rapidly, demonstrating a clear response.
This sense of touch is distributed across their entire body, not localized to a single organ. Beyond the tube feet, structures like spines and small, pincer-like pedicellariae also contribute to tactile perception. Pedicellariae help keep the sea star’s surface clean and can snap shut when stimulated. Sea stars can also detect subtle water currents and vibrations, which indicate the presence of nearby predators or prey.
Chemical Detection
Sea stars “smell” or “taste” their environment through chemoreception. This involves detecting dissolved chemicals in the water, which is important for their survival. This sense helps them locate food sources, such as shellfish, and can aid in finding mates or avoiding predators. Specialized cells on their tube feet and other body parts are responsible for this chemical sensing.
The tube feet constantly sample the surrounding water, being sensitive to chemical cues. This allows sea stars to follow chemical gradients or trails left by potential prey, guiding them to a meal. For instance, they might retreat from the chemical scent of a hungry crab, demonstrating how this sense aids in predator avoidance. Sea stars can respond to very dilute solutions of compounds, showing the precision of their chemical detection.
Light Perception
Even without complex, image-forming eyes, sea stars detect light. At the tip of each arm, they have simple photoreceptors known as “eye spots.” These eye spots are composed of many individual light-sensing units, or ommatidia, rather than a single lens. Their function is to distinguish between light and dark and to sense changes in light intensity and shadows.
This basic light detection allows sea stars to orient themselves, perceiving the general direction of light and seeking shelter. While they cannot form detailed images, some sea star species can form crude images, assisting them in staying close to preferred habitats like coral reefs. Eye spots at the end of each arm allow sea stars to bend their arms, stabilizing their gaze and enhancing perception of large structures. Deep-sea sea stars, living in perpetual darkness, possess functional eye spots, suggesting an ability to detect faint bioluminescence.