Sea Stars (Starfish)

You probably know sea stars as starfish, the name sea stars are commonly known by. But sea stars aren’t really fish. Sea stars, like sea urchins and sand dollars, do not have backbones, which makes them part of a group called invertebrates. Fish have backbones, which makes them vertebrates. Got it?

There are more than 1,600 species (types) of sea stars living in all the world’s oceans. Sea stars occupy every type of habitat, including tidal pools, rocky shores, sea grass, kelp beds, and coral reefs. Some sea stars even live in sands as deep as 20,530 feet (9,000 meters).

Most sea stars sport spiny skin and five arms, although some can grow as many as 50 arms. The arms are covered with pincer-like organs and suckers that allow the animal to slowly creep along the ocean floor.

Light-sensitive eyespots on the tips of the arms help the sea star find food. Favorites on the menu include mollusks such as clams, oysters, and snails.

The sea star eats by attaching to prey and extending its stomach out through its mouth. Enzymes from the sea star’s stomach digest the prey. The digested material enters the sea star’s stomach. Tiny organisms can be swallowed whole.

Sea stars aren’t social creatures, but they will congregate in large groups during certain times of the year to feed.

FAST FACTS
The scientific name for the bat sea star, found along the Pacific coast of North America, is Patiria miniata.

Sea stars can grow a new arm if they lose one, although sea stars generally have few predators thanks to their rigid bodies. 

Adult sea stars exist in a range of colors, from orange to pink to brown. They can grow from 0.4 inches (1 centimeter) to more than 3 feet (91 centimeters) across!

It’s difficult to tell whether a sea star is male or female just by looking at them.