Starfish underwater

Starfish are marine echinoderms known for radial symmetry and remarkable regeneration. Found in oceans worldwide, they inhabit shallow reefs to abyssal depths.

About this subject

Starfish, or sea stars (class Asteroidea), are echinoderms with a star-shaped body comprising a central disc and arms, typically five. They possess a calcareous endoskeleton and tube feet that aid in locomotion and feeding. Over 1,500 species inhabit oceans at all depths and salinities.

These animals play a crucial ecological role as predators, controlling populations of mollusks and sea urchins, especially on coral reefs. Some species can evert their stomachs to digest prey externally, such as mussels and oysters. Diet varies by species, including carnivores and detritivores.

Regeneration is one of their most remarkable features. A detached arm can regenerate a complete new body if it includes part of the central disc. This process takes weeks to months. They reproduce both sexually (spawning gametes) and asexually (fission). Interestingly, larvae are planktonic and undergo metamorphosis to adult form.

Unfortunately, starfish face threats like sea star wasting syndrome, causing lesions and mass die-offs, exacerbated by ocean warming. Culturally, they are marine icons, often associated with coastal environments and kept in aquaria. Despite the common name, they are not fish: they belong to phylum Echinodermata, closely related to sea urchins and sea cucumbers.

Frequently Asked Questions

Why can starfish regenerate lost arms?

They have pluripotent stem cells in the central disc and arms, enabling tissue regeneration. As long as part of the central disc remains, an arm can develop into a complete new individual.

What do starfish eat?

Most are carnivorous, feeding on mollusks, sea urchins, and crustaceans. Some species are detritivores or filter feeders. They can evert their stomachs to digest prey externally.

Are starfish fish?

No. They belong to phylum Echinodermata, while fish are vertebrates. They are more closely related to sea urchins and sea cucumbers.