# Starfish (*Asteroidea*)

> Starfish, also called sea stars, are marine invertebrates of the class Asteroidea, easily recognised by the five arms radiating from a central disc. They are echinoderms rather than fish, and creep slowly across the seabed on hundreds of tiny tube feet. Most species measure 12 to 25 cm across, prey on clams and mussels, and can regrow lost arms. Depending on the species they live anywhere from about 5 to 35 years.

- **Category:** Invertebrate
- **Conservation status (IUCN):** Least Concern
- **Range:** Ocean floors worldwide, from tide pools and coral reefs to the cold deep sea.
- **Canonical page:** https://globalanimalguide.org/animals/starfish/
- **Last reviewed:** 2026-07-16

## Scientific classification

- **Kingdom:** Animalia
- **Phylum:** Echinodermata
- **Class:** Asteroidea

## Facts at a glance

| Attribute | Value |
| --- | --- |
| Scientific name | Asteroidea (class) |
| Diet | Carnivore (mollusks, clams, mussels) |
| Habitat | Ocean floors, from tide pools to the deep sea |
| Lifespan | 5–35 years depending on species |
| Size | Commonly 12–25 cm (5–10 in) across |
| Top speed | Very slow; centimeters per minute |
| Conservation status | Least Concern (IUCN, most species) |

## An echinoderm, not a fish

Although they are often called starfish, sea stars are not fish at all but echinoderms, relatives of sea urchins and sand dollars. There are roughly 2,000 species in the class Asteroidea, found in every ocean from shallow tide pools to the deep sea. Most have five arms arranged around a central disc, though some species carry many more. Instead of a backbone they have a tough, spiny skin and a body plan built around radial symmetry.

## Life on tube feet

A sea star moves using a unique hydraulic system called the water vascular system, which powers hundreds of tiny tube feet on the underside of its arms. By pumping seawater through this network, it extends and grips with these feet to crawl slowly across the seabed. Movement is gentle and unhurried, measured in centimetres per minute rather than any real speed. The same tube feet also grip prey and help the animal cling to rocks against the pull of waves.

## Feeding on shellfish

Sea stars are carnivores, and many specialise in eating molluscs such as clams, mussels and oysters. To open a shell, a sea star wraps its arms around the prey and uses its tube feet to prise the two halves slightly apart. It then pushes its stomach out through its mouth and into the gap, digesting the soft body inside the shell before drawing the stomach back in. This unusual method lets it feed on prey far larger than its own mouth.

## Regeneration and survival

One of the sea star's most remarkable abilities is regeneration. If it loses an arm to a predator, it can slowly regrow the missing limb over months, and in some species a detached arm containing part of the central disc can even grow into a whole new animal. This power helps sea stars survive attacks that would kill many other creatures. Combined with lifespans that reach up to about 35 years in some species, it makes them tough, long-lived residents of the seabed.

## Habitat and diversity

Sea stars live on ocean floors worldwide, from rocky tide pools exposed at low tide to the cold, dark depths thousands of metres down. They come in a huge range of colours and sizes, though most species measure about 12 to 25 cm from arm tip to arm tip. Some are drab and well camouflaged while others are vivid orange, red, blue or purple. Their spiny skin and, in some species, mild toxins help protect them from predators.

## Reproduction

Most sea stars reproduce by releasing eggs and sperm into the water, where fertilisation takes place and tiny larvae drift as plankton before settling on the seabed. Many species can also reproduce asexually by splitting or by regenerating from a fragment of the body. A single large female may release millions of eggs in a season, though very few survive to adulthood. This mix of sexual and asexual strategies helps sea stars colonise new areas and recover from losses.

## Frequently asked questions

### Is a starfish a fish?

No. Despite the name, a starfish is not a fish but an echinoderm, in the class Asteroidea. It is more closely related to sea urchins and sand dollars, and it crawls on tube feet rather than swimming.

### How do starfish move?

Starfish move using hundreds of tiny tube feet on the underside of their arms, powered by a water vascular system. They crawl very slowly across the seabed, measured in centimetres per minute.

### What do starfish eat?

Starfish are carnivores that often feed on molluscs such as clams, mussels and oysters. A sea star prises the shell open and pushes its stomach out to digest the soft body inside.

### Can a starfish regrow a lost arm?

Yes. Starfish can regenerate arms lost to predators over several months. In some species, a detached arm that includes part of the central disc can even grow into an entirely new animal.

### How long do starfish live?

Lifespan varies by species, ranging from about 5 to 35 years. Larger, deep-water species tend to be the longest-lived.

### How big do starfish get?

Most starfish measure about 12 to 25 cm across from arm tip to arm tip, though size varies widely between the roughly 2,000 species.

## Sources

- [IUCN Red List — Asteroidea.](https://www.iucnredlist.org/search?query=Asteroidea&searchType=species)
- [Wikipedia — Starfish.](https://en.wikipedia.org/wiki/Starfish)

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Source: Global Animal Guide (https://globalanimalguide.org/animals/starfish/). Licensed CC BY-NC 4.0 — free for non-commercial reuse with attribution.