Asterina gibbosa

Geographic Range

The cushion star inhabits the regions of Europe's rocky coasts, most commonly the seas to the south and west of the British Isles.

• Biogeographic Regions
• atlantic ocean atlantic ocean
  • native native

Habitat

The cushion star commonly occupies shallow rock pools underneath stones, boulders, and overhangs that provide shelter. Other preferred sites include nestling among algae, sponge masses, or on cliff faces. The cushion star is vertically distributed between the depths of sea level and the intertidal to 130 meters, yet littoral cushion stars are only found in rock pools and relatively damp habitats. This vertical distribution may be extended on shores with rock pools, but this extension will not go beyond the high-water-neap-tide level due to an intolerance to dessication at high temperature, inadequate food supply, and complex behavioral responses to gravity and light. Comparative studies on the ecology of the cushion star at Lough Line showed that A. gibbosa are found in the rocky shallow sub-littoral in varying abundance, yet it was absent from any of the outer shore sites.

• Habitat Regions
• temperate temperate
• saltwater or marine saltwater or marine

• Aquatic Biomes
• temporary pools
• coastal coastal

• Other Habitat Features
• intertidal or littoral intertidal or littoral

Physical Description

Asterina gibbosa is a pentagonal shape with five short arms and a diameter up to 6 cm. The tiny, blunt-armed cushion star ranges in color from greenish-gray, yellowish-green, to reddish-brown. The asteroids are considered a slow moving species with the cushion star being the slowest among all, moving approximately 2.5 cm per minute. The cushion star resembles its given name since the body appears to be inflated like a pillow cushion, emphasizing it small size and blunt arms. The class that the cushion star belongs to, Crinoidea , has retained an upwardly-directed mouth. The cushion star has a body consisting of a tiny central disk to carry the main organs. The mouth of the cushion star is located in the center of the underside. Located on the underside of each arm are grooves that lead to the center that contain hundreds of tube-feet.

• Other Physical Features
• ectothermic ectothermic
• heterothermic heterothermic
• radial symmetry radial symmetry

Development

Eggs are usually laid on the underside of stones by female Asterina gibbosa . Up to three weeks later, the young hatch bipinnaria and later into brachiolaria larvae. The larvae are bilaterally symmetrical and metamorphose into juveniles.

• Development - Life Cycle
• metamorphosis metamorphosis

Reproduction

The cushion star is one of the few sequential hermaphroditic echinoderms. Younger and smaller individuals are males, developing into females as they increase in size and age. Male and female gametes are not readily distinguishable to the naked eye. One would have to see the gonads or see them actually spawning. The gonads on the cushion star are located in each arm. These gonads release the gametes through gonaducts that are located on the central body between the arms. The male gametes are produced first and later only female gametes are produced. Female A. gibbosa deposit up to 1000 eggs in a specific location (usually underside stones) to the ground in the process of reproduction. At the beginning of reproduction, many starfish belonging to the asteroid species form aggregations. In Asterina gibbosa , several males surround or congregate around one female during reproduction.

• Key Reproductive Features
• sequential hermaphrodite
  • protandrous protandrous
• sexual sexual
• fertilization fertilization
• oviparous oviparous

There is no post-spawning parental investment.

• Parental Investment
• pre-fertilization
  • provisioning

Lifespan/Longevity

Cushion stars can live up to seven years.

Behavior

The cushion star is mobile, but not quick. Since it has a speed of only 2.5 cm per minute, this starfish is the slowest of its class. This lack of speed and agility is due to the length of its rays and the thickness of its body. Asterina gibbosa is extremely sensitive to light and temperature, resulting in its preference to sheltered areas of habitation. Studies conducted to observe factors affecting the respiraion of intertidal A. gibbosa showed that the aquatic and aerial oxygen uptake by this species was low when compared with other intertidal invertebrates. The studies also concluded that small cushion stars were less temperature-dependent than larger cushion stars, regarding aquatic oxygen uptake.

Communication and Perception

In general, echinoderms have nerve nets and non-centralized nervous systems. Asteroids have optic cushions, or eyespots, and respond to light. Echinoderms in general respond to chemicals, light and touch.

• Communication Channels
• chemical chemical

• Other Communication Modes
• pheromones pheromones

• Perception Channels
• visual visual
• tactile tactile
• chemical chemical

Food Habits

Cushion stars are omnivorous. As with other starfish A. gibbosa feed themselves by inverting their stomachs in order to digest the food they eat. Their diet includes molluscs, worms and ophiuroids that are also found among rocky shores. They also eat microorganisms, decaying seaweeds and dead invertebrates.

• Primary Diet
• carnivore carnivore
  • eats non-insect arthropods
  • molluscivore molluscivore
  • vermivore
  • eats other marine invertebrates
• omnivore omnivore
• detritivore detritivore

• Animal Foods
• carrion carrion
• mollusks
• aquatic or marine worms
• echinoderms
• other marine invertebrates

• Plant Foods
• macroalgae macroalgae

• Other Foods
• detritus detritus
• microbes

Predation

Starfish are most vulnerable in their larval stage. Few young survive to adulthood.

Economic Importance for Humans: Positive

The cushion star does not have any positive effects on humans.

Economic Importance for Humans: Negative

The cushion star does not have any adverse effects on humans.

Conservation Status

The species is not threatened, but an oil spill at the entrance to Milford Haven in February 1996 spread of 70,000 tons of oil along the Pembrokeshire coast. This location had a major population of Asterina gibbosa which was greatly affected because of the spill. However, observations were made eight weeks after the incident, and there was a good survival of the larger Asterina gibbosa , even some living near small pockets of oil underneath rocks.

Additional Links

Encyclopedia of Life

Contributors

Renee Sherman Mulcrone (editor).

Estella King (author), Southwestern University, Stephanie Fabritius (editor), Southwestern University.

References

Barrett, R. 1997. "Echinodermata: Cushion Stars" (On-line). Excerpted from The Oxford Interactive Encyclopedia. Accessed December 14, 2004 at http://ourworld.compuserve.com/homepages/BMLSS/cushion.htm .

Brusca, R., G. Brusca. 2003. Invertebrates . Sunderland, Massachusetts: Sinauer Associates, Inc..

Crump, R., R. Emson. 1996. "Oral Contribution: Observations on the Effects of the" (On-line). Accessed February 16, 2001 NO LINK at http://www.calacademy.org/research/izg/echinoderm/conference/ .

Dale, J. 2000. "Starfish Reproduction" (On-line). Starfish science. Accessed December 14, 2004 at http://www.vsf.cape.com/~jdale/science/reproduction.htm .

Emson, R., R. Crump. 1984. Comparitive Studies on the Ecology of *Asterina Gibbosa* and *A. Phylactica* at Lough Line. Journal of the Marine Biological Association of the United Kingdom , 64: 35-53.

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

Marlin, 11/24/04. "Cushion Star, Asterina gibbosa" (On-line). Marlin, the marine life information network for Britain and Ireland. Accessed December 14, 2004 at http://www.marlin.ac.uk/learningzone/species/LZ_Astgib.htm .

Murphy, C., M. Jones. 1987. Some Factors Affecting the Respiration of Intertidal *Asterina Gibbosa*. Journal of the Marine Biological Association of the United Kingdom , 67: 717-727.

Nichols, D., J. Cooke. 1971. The Oxford Book of Invertebrates . Oxford: Oxford University Press.

Picton, B. E., 2002. "A Field Guide to the Shallow-Water Echinoderms of the British Isles" (On-line). Asterina gibbosa. Accessed December 14, 2004 at http://www.habitas.org.uk/marinelife/species.asp?item=ZB1130 .

Skewes, M. 11/10/2002. "Asterina gibbosa. A cushion star" (On-line). Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme. Accessed December 14, 2004 at http://www.marlin.ac.uk/species/Asterinagibbosa.htm .