Starfish

MarineEchinodermInvertebrate

Overview

Starfish, also called sea stars, are marine animals in the class Asteroidea, part of the echinoderm group that also includes sea urchins and sea cucumbers. There are thousands of species. This page is a group-level overview. Most have a central disc and five arms, though some have many more. Because they are not fish, many scientists prefer the name "sea star".

Habitat & Range

Starfish are found only in the sea, never in fresh water, and live on the seabed from rocky shores and tide pools to coral reefs and the deep ocean floor. Different species are adapted to different depths, temperatures, and substrates, so habitat varies considerably across the group. Some are common in the intertidal zone, where they can be exposed at low tide.

Diet

Many starfish are carnivores or scavengers. A number of species feed on shellfish such as mussels and clams, and some can push their stomach out through their mouth to digest prey externally. Others graze on algae, sponges, or detritus. Feeding strategies vary widely by species; the crown-of-thorns starfish, for example, is a notable coral predator.

Behavior

Starfish move using hundreds of tiny tube feet on the underside of their arms, powered by an internal water-based hydraulic system called the water vascular system. They are slow-moving but can right themselves if turned over and grip surfaces firmly. Many starfish can regenerate arms lost to predators or injury, and in some species a detached arm can even regrow into a new individual.

Human Interaction & Conservation

Starfish are an important part of many seabed ecosystems, and some are considered keystone predators whose feeding shapes the community around them. A few, such as the crown-of-thorns starfish, can damage coral reefs during population outbreaks. Some sea-star populations have also been hit by disease events. Conservation status varies by species and for most is not well established, so it should not be assumed.

Similar Animals

Starfish are echinoderms, related to brittle stars, sea urchins, sand dollars, and sea cucumbers. Brittle stars look similar but have a small disc with thin, snake-like arms and move quite differently. Despite the shared "star" shape, starfish are unrelated to jellyfish or other groups covered on FaunaHub.

More photos of the starfish