Common starfish, Asterias rubens

Sea stars have the body covered with short and rounded limestone plates. They have radial symmetry, that is to say, they are organized into five axes. They have five flexible arms around a central disk. This starfish is the most common srarfish in the St. Lawrence. Arms are rather flat and wide. Its spines are pale and form a line on top of the arm. It measures up to 40 cm in diameter. Its color is not always purple, it can be in shades of brown, red, orange, yellow or purple.

Because starfish fear of exposure to air, they are usually found below the limit of low tide or hidden under algae at low tide. The can be foud as deep as 350m.

Their way of moving very slowly is achieved through a pumping system and hundreds of feet ended by little suckers (the tube feet) beneath their bodies. If the star is turned on it's back, it remains motionless at first, then it's tube feet will try to make contact with the ground by bending. Once contact is established and it has a sufficient number of attachments, it turns and goes off in search of food. Most of the stars eat through a mouth connected almost directly to their stomach. Some stars can get their food through a microscopic mucus on their skin as the blood-red starfish. The organic material is then adhered to the mouth carried by motile cilia. If the mouth can come into contact with the desired food, the stomach is then projected outwards from the mouth to digest everything. Thus a star may devour a shell by sliding it's stomach between two shells held open by the force of his arms and digest all on site. To open a bivalve, the star must maintain traction on the valves tirelessly until the mollusk give up.

The stars reproduce asexually by breaking into two parts more or less equal. In sexual reproduction, they stand on their five arms and lay in two hours, more than 2 million eggs while the males unleash their sperm. Fertilized eggs become larvae that float in water for some time before settling at the bottom of the sea to become baby starfish Only one egg in a million becomes an adult.

Stars can do self-mutilation to escape their predators. Then they are able to regenerate. An star can regenerate an arm if it has a sufficient portion of the central disk.

Oyster breeders have tried to get rid of stars by cutting them in half with a hatchet, but in reality, they multiplied their problem.

The stars are carnivores. Some feed exclusively on sponges, but most eat all that passes under their feet, shellfish, sea urchins, sea cucumbers, dead fish or even other sea stars, they can consume up to 10 shells per day.

They are found in the estuary, the Gulf of St. Lawrence and along the Atlantic coast.

DORIS 28/07/2008: Asterias rubens Linnaeus, 1758, http://doris.ffessm.fr/fiche2.asp?fiche_numer...

Editors: Sandra D'Aoûst / Sophie Paré
Translation : Blaise Barrette

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