The Life of a Starfish: Movement, Feeding, and Survival in the Sea

One of the most unusual and captivating animals to ever live in our planet’s vast seas, Starfish, also known as sea stars, are marine invertebrates that belong to a group of animals known as echinoderms. Echinoderms have radial symmetry, unlike most animals, which have bilateral symmetry. The Echinodermata phylum also includes sea urchins, sea cucumbers, and sand dollars. While the smallest starfish are less than an inch in diameter, the largest species can be over three feet across. But lacking teeth or a jaw, how do starfish eat? Discover not only how starfish eat, but what they eat, as we take a deep dive into the diverse diet of starfish.

How Starfish Eat

Starfish don’t digest food inside their bodies as most animals do. They expel their entire stomach through their mouth in a process known as eversion.

Starfish scoot along the sea floor using hundreds of tiny structures called tube feet attached to the bottom of each of their arms. Filling these tiny feet with water while alternately contracting and relaxing them allows starfish to move surprisingly quickly from place to place. When a starfish finds something it wants to eat, it will quickly propel itself toward its prey.

A starfish’s mouth is located on the underside of its body, at the center where its limbs meet. From its mouth, a starfish will extend its stomach, completely enveloping its prey. The stomach then secretes digestive enzymes to break down the prey, making it easier to pull back into the starfish’s mouth. With the prey animal trapped inside, the starfish’s internal digestive glands continue to break it down.

What Starfish Eat

Of the roughly 2,000 species of starfish, nearly all of them are carnivorous. This means they feed primarily on the flesh of other animals living in the ocean. 

A starfish’s diet is composed of various species of shelled mollusks, which the starfish break open with their powerful, suction-cupped feet. However, they are known to feed other small prey animals, including clams, mussels, sponges, oysters, snails, worms, coral, sand dollars, barnacles, plankton, crabs, and shrimp. They will also eat other starfish.

Starfish Predators

Starfish have a few helpful defense mechanisms that can keep predators away. Most notably, they have a very rough, bone-like exoskeleton that is unpalatable to many animals. Additionally, the suction cup-like structures on their limbs make them very difficult to peel off surfaces like rocks.

Despite these adaptations, starfish are preyed upon by a wide range of animals, including sharks, crabs, rays, octopuses, snails, turtles, otters, seabirds, and fish.

Summary of What Starfish Eat

Here’s a recap of the foods that starfish commonly consume: