Sea Stars
(Asteroidea)
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Animal Type
Invertebrates
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Exhibits
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Range
Arctic Ocean
Atlantic Ocean
Indian Ocean
Pacific Ocean
Southern Ocean
Overview
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!
A Note From the Caretaker
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.
Quick Facts
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.
Explore Exhibit Residents
Learn more about the animals that share an exhibit with this one.
Anemones (Actiniaria)
Sea anemones are named after and resemble flowers.
Atlantic Puffin (Fratercula arctica)
Atlantic puffins have a distinctive large, triangular red-orange bill with a blue-gray base and yellow ridge.
Banggai Cardinalfish (Pterapogon kauderni)
These fish hide among the spines of sea urchins for protection.
Horn Shark (Heterodontus francisci)
The horn shark gets its name from the short venomous "horn" in front of each of its dorsal fins.
Percula Clownfish (Amphiprion percula)
Learn about percula clownfish, including their habitat, diet, range and population status, and where you can find them at the National Aquarium.