Starfish underwater

Starfish are marine echinoderms with radial symmetry and remarkable regenerative abilities.

About this subject

Starfish belong to the phylum Echinodermata, class Asteroidea, and are relatives of sea urchins and sea cucumbers. They inhabit all oceans, from intertidal zones to abyssal depths. There are about 1,500 known species, ranging from a few centimeters to over a meter in diameter. Despite their name, they are not fish; they lack gills, fins, or an internal bony skeleton.

One of the most fascinating aspects of starfish is their regenerative capacity. Many species can regrow lost arms, and in some cases, a single arm with part of the central disc can develop into a new individual. This process can take months or years. Additionally, they have a water vascular system that allows them to move and capture prey, such as mollusks, using suction cups on their tube feet.

Ecologically, starfish are considered ecosystem engineers. The species Pisaster ochraceus, for example, controls mussel populations on rocky shores of the North Pacific, maintaining local biodiversity. Without this predator, mussels would dominate, suffocating other species. In Brazil, species like the spiny starfish (Echinaster brasiliensis) are common along the coast.

Fun facts: starfish have no brain or blood; their body fluid, coelomic fluid, circulates through the body. They breathe through papulae, small projections on the surface. Some species can evert their stomach through their mouth to digest prey externally. Although they are symbols of healthy marine life, their populations are threatened by diseases like sea star wasting syndrome, which has devastated colonies in the Pacific.

Frequently Asked Questions

Are starfish fish?

No, they are echinoderms, belonging to the phylum Echinodermata. They lack gills, fins, and an internal bony skeleton, which are typical of fish.

How do starfish regenerate?

Many species can regrow lost arms. In some cases, a single arm with part of the central disc can develop into a new individual. The process depends on the species and environmental conditions.

What is the ecological importance of starfish?

They act as keystone predators in many marine ecosystems, controlling populations of mollusks and sea urchins. Their presence helps maintain biodiversity on reefs and rocky shores.