Starfish underwater

Starfish are marine echinoderms found in all oceans, known for their remarkable regenerative abilities and wide diversity of colors and shapes.

About this subject

Starfish, also known as sea stars, belong to the class Asteroidea within the phylum Echinodermata, which also includes sea urchins and sea cucumbers. There are approximately 1,500 living species, inhabiting a range of environments from intertidal zones to abyssal depths. They move using a hydraulic water vascular system and tube feet equipped with suction cups. While most species have five arms, some, like the sunstar, can possess up to 40 arms.

One of their most remarkable traits is regeneration. If a starfish loses an arm, it can grow a new one. In certain species, a detached arm containing part of the central disc can regenerate into an entire new individual. This capability relies on totipotent cells and the distribution of organs across the arms. The regeneration process may take months or years depending on the species and environmental conditions.

Starfish are primarily carnivorous, feeding on mollusks such as mussels and oysters. They use their arms to pry open shells and then evert their stomach to digest the prey externally. This feeding behavior significantly influences reef ecosystems and mollusk populations, making them keystone species in many habitats. Notably, starfish lack a brain and blood; they have a simple nervous system and rely on coelomic fluid for oxygen and nutrient transport.

In Brazil, species like the reticulated starfish (Oreaster reticulatus) are common along the northeastern coast. However, populations face threats from reef degradation, pollution, and collection as souvenirs. Recent research suggests that ocean acidification may hinder the formation of their calcareous skeleton, raising concerns about their long-term survival.

Frequently Asked Questions

How many arms can a starfish have?

Most have five arms, but some species like the sunstar can have up to 40 arms. The number varies by species.

Can starfish regenerate?

Yes. They can regenerate lost arms. In some species, an arm with part of the central disc can grow into a new individual.

What do starfish eat?

They primarily eat mollusks such as mussels and oysters, using their arms to pry open shells and evert their stomach to digest prey externally.