Animal Diversity Web

Geographic Range

Asterias rubens inhabits the waters of the Atlantic Ocean, and is an Arctic boreal species that can withstand temperatures up to 22 degrees Celcius It can be found in the stretch of ocean from the White Sea to Senegal. It is the most prevalent conventional starfish of the Northeast Atlantic Ocean (Grzimek 1972; Horton 2000).

• Biogeographic Regions
• arctic ocean
  • native
• atlantic ocean
  • native

Habitat

Individuals of Asterias rubens live in depths ranging from sea level to 650 feet below sea level. When Asterias rubens is especially abundant in the British Seas, many can be found on the shoreline. Asterias rubens is commonly found on rocks, sand, mud flats, and in beds of mussels. These areas provide a good source of food for the starfish. (Grzimek 1972; Horton 2000) .

• Aquatic Biomes
• benthic
• coastal

Physical Description

The ceolomate, Asterias rubens, has a body which consists of a central disk with five arms radiating from it. These arms can reach 26 centimeters in length, allowing the body to reach lengths just over 50 centimeters across. Each arm has a radial canal running down the length of it with paired side braches. These branches are connected to the ampulla and tube feet. Asterias rubens is covered in tube feet which help in locomotion, respiration, and with suction. The radial canals are connected to the circumoral canal. This makes up the water-vascular system which is part of the coelom. At the end of each arm an eye spot can be found which allows the starfish to sense light. The body is also covered in cilia which helps trap small organisms to be digested. Under the surface of the skin lie hard calcium plates called ossicles. Asterias has no head, but its mouth can be found on the lower, oral side of the body where the ambulacral grooves from each arm meet. Asterias rubens exhibits radial symmetry in the adult form, although it has bilateral symmetry as a larva. The species Asterias rubens varies in color. It can range from orangish brown, to reddish brown, and even reddish violet (Grzimek 1972; Hunter-Russel 1979; Larousse 1967; Nichols 1979).

• Other Physical Features
• ectothermic

Reproduction

In Asterias rubens, the sexes are separate. Each of its five arms contains two gonads on the oral side of the body. These gonads have gonopores which provide a pathway for the eggs or sperm to get to the exterior of the body. This is neccessary because fertilization is external. When eggs are released into the sea, the neighboring females are stimulated to release their eggs as well. The release of the eggs stimulates the males to release sperm into the sea. An average of two-and-a-half million eggs are released at one time from each female. These eggs develop into bipinnaria larvae in the Asterias rubens. The larvae often swim about for a period of up to three weeks before settling. Once the larvae has settled, it metamorphoses into what we think of when we think of starfish. The Asterias rubens is also capable of regenerating up to four arms that have been lost. This is taken advantage while in the process of escaping predators. The arm can be lost without creating too many problems for the future life of the starfish because it can grow back (Hunter-Russel 1979; Larousse 1967).

Behavior

Asterias rubens uses its many tube feet to help it move around in search of food and to escape from predators. On the end of each of its tube feet lies a vacuum-cup sucker which is used for traction and leverage in the process of locomotion. Because the Asterias, like all starfish, have only longitudinal muscle, the tube feet are only able to contract or withdrawl. Through these contractions, the Asterias is able to grasp onto the surface and pull itself along. This process is very slow, but speeds up as the independent tube feet begin working in unison. The Asterias moves at an average of six inches per minute in a straight line. Although they may appear to look like a wheel, they do not move in wheel-like action. Tube feet also aid the Asterias in righting itself if it gets turned over. To do this the starfish turns one of its arms over, allowing the tube feet to grip the rock or sand surface. Once a grip is established, the arm turns more and more, allowing other tube feet to grip the surface. This continues as other arms join in. Eventually, the Asterias regains its upright position.

During times of intense turbulence in the sea, the tube feet come to the aid of the Aterias rubens. While other animals much retreat to crevices, the starfish uses it tube feet to secure itself to the surface. Once that has been accomplished, it pushes its body against the surface as much as possible in an attempt to flatten out. This is helpful for the slow-moving starfish when large waves come (Larousse 1967; Hunter-Russel 1979).

Food Habits

Asterias rubens, like most other starfish species, is carnivorous. It often feeds on bivalves, gastropods, and crabs. Asterias rubens makes use of its strong arms and tube feet while preying on bivalves like mussels. The suction on the tips of the tube feet allow it to have a firm grasp on its prey. The arms then pull the two halves of the shell apart exposing the inside of the shell. Asterias rubens then extrudes its stomach from the mouth on the lower, oral side of the body. The stomach, turned inside out, goes into the gap between the shell halves. A gap of only 0.1 mm is needed for the Asterias to get its stomach inside the shell and wrap it around the soft body of the prey. At this time gastric juices are expelled, allowing for the process of digestion to occur. It is also thought that these juices contain toxins which debilitate the prey. Asterias has neither jaws nor teeth so it must wait until the prey is digested into a soft mass before it pulls its stomach back inside of its body. The nutrients are moved about the body through diffusion. Coeomic fluid aids in this process. Any undigested materials are expelled from the stomach while it is out of the body (Nichols 1979; Larousse 1967; Hunter-Russel 1979).

Economic Importance for Humans: Positive

Asterias rubens is a beautiful animal that fascinates both young and old. When most people think of a starfish, it is Asterias rubens that comes to mind. While this starfish may not have a tangible benefit to humans, it has a great psychological one. Its uniqueness in comparison to other species is great. This significance leads to the purchase of starfish memorabilia.

Currently much research is being to done to find if there are any beneficial uses of this species. This is especially true for the medical industry. Asterias rubens is used as a component in some homeopathic remedies.

• Positive Impacts
• body parts are source of valuable material

Economic Importance for Humans: Negative

This species does not directly harm humans in any way. It does not have poisons or bites that could be harmful to swimmers. It does not harm any of the man-made structures in the ocean, nor does it cause damage to the surroundings such as the vegetation. The only negative effect that this species could possibly have would involve the consumption of clams and other bivalves that humans like to eat. These are the prominent food source of Asterias rubens as well. Unless the population of Asterias rubens gets out of control, there should not be any measurable effect to the sea food supply of humans.

Conservation Status

Asterias rubens is not currently under any restrictions, nor is it on any of the endangered species lists.

• IUCN Red List

  No special status

• US Federal List

  No special status

• CITES

  No special status

Contributors

Brooke Chidgey (author), Southwestern University, Stephanie Fabritius (editor), Southwestern University.

References

Grzimek, B. 1972. Grzimeks's Animal Life Encyclopedia. New York: Van Nostrand Reinhold Company.

Horton, A. 2000. "British Marine Life Study Society" (On-line). Accessed February 16, 2000 at http://ourworld.compuserve.com/homepages/BMLSS/Asterias.htm.

Hunter-Russel, W. 1979. A Life of Invertebrates. New York: Macmillan Publishing Co. Inc.

Larousse, 1967. The Larousse Encyclopedia of Animal Life. New York: McGraw-Hill Book Company.

Nichols, D. 1979. Oxford Book of Invertebrates. New York: Oxford University Press.