Sea stars are invertebrates related to sea urchins, sea cucumbers and sand dollars, which are all echinoderms. Echinoderm means spiny skin—a reference to their hard, calcified skin, which helps to protect them from predators.
Sea stars have rows of tiny tube feet extending from the grooved surface on their underside. These tube feet allow them to crawl along the ocean floor via suction created by an internal water-driven hydraulic system. These animals also have an amazing ability to regenerate arms when they are severed, or even a new body in some species. All of their vital organs are located in the arms, so a portion of an arm could potentially grow a whole new sea star.
There are close to 2,000 species of sea stars in the world’s oceans. Most species have five arms, but some have many more—even as many as 40! At the Aquarium, you can see 10 species of sea stars throughout the exhibits. Look closely in the Kelp Forest to spot the sun sea stars, which sport 20 arms each!
Sea stars are mostly carnivorous and prey on mollusks—such as clams, mussels, and oysters—which they pry open with their suction-cupped feet. At the Aquarium, we feed some of our sea stars pieces of fish and shrimp, but the majority of our sea stars feed on detritus, which helps to keep our exhibits clean.
Sea stars have a peculiar way of eating. They actually digest their prey outside of their bodies by extruding their stomach out through their mouth and enveloping the prey item. When the meal is digested, the stomach is drawn back into the body.
The smallest sea stars are less than an inch in diameter, while the largest sea stars can reach up to 3 feet in diameter.
Sea stars live in saltwater and are found in all of the world’s oceans, from warm, tropical waters to the cold seafloor.
Many different animals eat sea stars, including fish, sea turtles, snails, crabs, shrimp, otters, birds and even other sea stars. Though the sea star’s skin is hard and bumpy, a predator can eat it whole if its mouth is large enough. Predators with smaller mouths can flip the sea star over and eat the softer underside.
Back to the Top