The common sea star is a sea star characteristic of European coasts. Its body consists of a central disc from which five robust arms generally extend. These arms can reach around 12 inches in length, giving the animal a span of more than 20 inches in large individuals.

Its coloration is variable and can range from orange-yellow to reddish brown, with shades of purplish red also occurring. Its upper surface is covered with small calcareous spines, while its underside bears numerous tube feet arranged along the arms. These small appendages allow it to move, grip the substrate firmly and manipulate its prey.

At the tip of each arm is also a small light-sensitive structure that allows it to perceive changes in light intensity.

The common sea star inhabits the temperate to cold waters of the North Atlantic ocean. It occurs along the coasts of Europe, from Arctic regions and the White Sea to the Strait of Gibraltar, as well as along the northwestern coast of Africa as far south as Senegal.

It is particularly common in the northeastern Atlantic, especially around the British Isles, in the North sea and along the French coast.

The common sea star lives on the seafloor, from nearshore waters to depths of several hundred feet. It can inhabit a wide variety of substrates, including rocky bottoms, sandy or muddy seabeds and areas where mussel beds develop.

It is particularly well adapted to coastal environments affected by tidal movements and can be observed in the intertidal zone when the tide recedes. Its numerous tube feet allow it to remain firmly attached to the seafloor, even when currents or waves become strong.

The common sea star is a carnivorous predator that feeds mainly on animals living on the seafloor. Mussels and other bivalves make up an important part of its diet, but it can also capture gastropods, small crustaceans and other invertebrates.

To open a mussel, it uses its arms and tube feet to gradually pull the two shell valves apart. Once a small opening has been created, it can evert its stomach through its mouth and insert it inside the shell. Digestive enzymes then begin breaking down the prey's tissues before the nutrients are absorbed. This feeding method allows it to consume animals much larger than its small mouth might suggest.

The common sea star primarily reproduces sexually through external fertilization. Males and females release their sperm and eggs directly into the seawater, where fertilization takes place. The fertilized eggs develop into tiny larvae that temporarily live in the water column. These larvae gradually develop before undergoing metamorphosis and taking on the characteristic shape of a young sea star.

The common sea star also has remarkable regenerative abilities and can regrow several arms after they have been lost.