Starfish underwater

Starfish, or sea stars, are marine echinoderms renowned for their remarkable regenerative abilities and diverse colors and shapes, inhabiting oceans worldwide.

About this subject

Starfish, also known as sea stars, are echinoderms belonging to the class Asteroidea, with about 1,500 species found in all the world's oceans, from tidal pools to deep-sea trenches. Despite their common name, they are not fish; they possess a unique water vascular system that powers hundreds of tiny tube feet on their underside, enabling locomotion and feeding.

One of their most extraordinary traits is regeneration. If a starfish loses an arm, it can regrow the entire limb, and some species can even regenerate a whole body from a single severed arm if part of the central disc is present. This ability helps them survive predators like sea otters and gulls, though regeneration takes months to years.

Their diet primarily consists of bivalve mollusks such as clams and oysters. They use their arms to pry open shells and then extrude their stomach to digest the prey externally. Some species are scavengers, while others feed on coral polyps or detritus. Ecologically, starfish are keystone species in many marine environments, controlling mussel populations and supporting biodiversity.

Reproduction usually involves external fertilization, with females releasing eggs and males releasing sperm into the water, producing planktonic larvae. A few species brood their young. Threats include climate change, ocean acidification, and habitat loss. Starfish are sensitive to environmental changes, making them useful indicators of reef health.

Frequently Asked Questions

How many arms can a starfish have?

Most species have five arms, but some have 10, 20, or even up to 40 arms, such as the sunflower sea star (Pycnopodia helianthoides).

Can starfish move quickly?

No, they move slowly using their tube feet, with a top speed of about 15 cm per minute in some species.

Why are starfish important to the ecosystem?

They control populations of mollusks and sea urchins, preventing overgrazing. In coral reefs, they help maintain ecological balance.