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 using 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 habitat to spot the sun sea stars, which have 20 arms each!
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 their habitats clean.
Learn more about sea stars! Did you know that sea stars have a peculiar way of eating? They digest prey outside of their bodies by extruding their stomach out through their mouth and enveloping their meal. Once the food is digested, their stomach is drawn back into their body.
Sea stars live in salt water and are found in all of the world’s oceans, from warm, tropical waters to the cold seafloor.
Sea stars are mostly carnivorous and prey on mollusks—including clams, mussels and oysters—which they pry open with their suction-cupped feet.
The smallest sea stars are less than an inch in diameter, while the largest sea stars can reach up to 3 feet in diameter.
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.