Starfish

Starfish—more accurately called sea stars—live on rocky shores, coral reefs, and deep-sea floors. Their bodies display radial symmetry, typically with five arms radiating from a central disk, though some species have many more. A tough, calcified skin protects them from predators. Instead of blood, sea stars circulate seawater through an internal hydraulic system called the water vascular system, which powers hundreds of tiny tube feet lining the underside of each arm.

Tube feet act like suction cups that allow sea stars to creep along surfaces, pry open clam shells, and cling to rocks against crashing waves. When a starfish wraps around a mussel, it uses hydraulic pressure to pull the shells apart slightly, then pushes its stomach outside its body to digest the prey externally before pulling the nutrients back in. Many species also scavenge on decaying animals, helping keep the seafloor clean.

Starfish can regenerate lost arms—and some can regrow an entire body from a single arm if part of the central disk remains. This ability helps them survive predator attacks and storm damage. However, crown-of-thorns starfish population booms can devastate coral reefs, so researchers monitor their numbers and manage outbreaks to prevent reef collapse.

Sea stars face threats from warming oceans, marine heat waves, and diseases such as sea star wasting syndrome, which causes lesions and rapid tissue breakdown. Conservationists improve water quality by reducing runoff, while aquariums engage citizen scientists to report sightings and health conditions. Researchers study starfish nervous systems to learn how decentralized control works, providing insights for robotics.

For students, tide pool explorations reveal how starfish share space with anemones, crabs, and sea urchins. Class projects might model the water vascular system using syringes and tubing or track recovery in areas affected by wasting events. Respectful touch—wet hands only—and returning sea stars to their exact resting spot protect these unusual animals so they can continue starring in ocean food webs.