Dendraster excentricus
Dendraster excentricus | |
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Ganges Harbour , British Columbia, Canada
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Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Echinodermata |
Class: | Echinoidea |
Order: | Clypeasteroida |
Family: | Dendrasteridae |
Genus: | Dendraster |
Species: | D. excentricus
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Binomial name | |
Dendraster excentricus Eschscholtz, 1831
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Synonyms [1] | |
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Dendraster excentricus, also known as the eccentric sand dollar, sea-cake, biscuit-urchin, western sand dollar, or Pacific sand dollar, is a species of sand dollar in the family Dendrasteridae. It is a flattened, burrowing sea urchin found in the north-eastern Pacific Ocean from Alaska to Baja California.
General information
Dendraster excentricus is an irregular
Description
They are colored gray, brown, black or shades of purple. Their size is variable, averaging 76 mm with the world's largest found measuring 120 mm wide.
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Dendraster Excentricus Sizes (World's Largest on Right)
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Test of a dead D. excentricus
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Oral side of D. excentricus
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Diagram of aboral side
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Diagram of oral side
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D. excentricus aggregation at low tide
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Comparison of test of Dendraster and sea urchin
Habitat
They are either found subtidally in bays or open coastal areas or in the low intertidal zone on sandy on the Northeast Pacific coast. They can live at a depth of 40 to 90 meters, but usually is found in more shallow areas. Sand dollars are usually crowded together over an area half buried in the sand. As many as 625 sand dollars can live in one square yard (0.85 sq m). It is the only sand dollar found in Oregon and Washington. It has been found on Burfoot Beach in the South Puget sound.
Behavior and feeding
Like its cousins, dendraster is a suspension feeder which feeds on
Hydrofoil design
This particular species of sand dollar is known for its curious behavior:
When exposed to a steady flow of water, they gather in groups, forming aligned rows in the sand, while digging their front edge in and raising their back edge into the flow of water, lined up so it passes from right to left across their bodies. Because the shape of a sand dollar is a hydrofoil, this draws particles of food closer in to their mouths during feeding, a benefit enhanced by the alignment of many individuals together into a communal feeding group.
Reproduction
Sexes are separate, with no noticeable differences in external features of the two sexes. Reproduction is sexual and D. excentricus reaches sexual maturity between 1 and 4 years of age, spawning in late spring and early summer. Fertilization is external, the female Dendraster discharges the eggs through her gonopores and they are fertilized by the male, who protrudes his genital papilla from his body wall. This is one reason they are believed to live in large groups and tend to release gametes at the same time into the water column. Eggs are pale orange, and are covered by a thick jelly coat which keeps adults from eating the eggs.
Development
The first larval stage is called a prism. After this stage the embryo will develop two arms transforming itself into an
Lifespan and predation
Predators include the seastar
Conservation
The habitat they live in on the sandy seafloor is sometimes damaged by bottom trawling, causing harm to many organisms. Ocean acidification and sea surface warming also harm populations of sand dollars.
References
- ^ Dave Cowles (2006). "Echinarachnius excentricus (Eschscholtz, 1831)". Walla Walla University. Archived from the original on June 2, 2010. Retrieved January 29, 2010.
- ^ # Sand dollar from Olympia beach may break a record HeraldNet, August 21, 2013
- OCLC 7043400.
- Dendraster excentricus Intertidal Marine Invertebrates of the South Puget Sound
- Dendraster excentricus Walla Walla
- Biogeography of the Western Sand dollar San Francisco State University
- Sand dollar, Monterey Bay Aquarium
- The persistence of a sand dollar, OnEarth.org
- Strathrnann M. 1987. Reproduction and Development of Marine Invertebrates of the Northern Pacific Coast. University of Washington Press, Seattle, Washington. 670 pp.
- Marin Jarrin, Jose R. "Embriogenesis and Larval Stages of Dendraster excentricus". 2007. University of Oregon, Eugene, Oregon.
- Smith, Andrew. 1984. Echinoid Palaeobiology. London: George Allen & Unwin.
Further reading
- Rich Mooi. "Sand Dollars of the Genus Dendraster (Echinoidea:Clypeasteroida): Phylogenetic Systematics, Heterochrony, and Distribution of Extant Species". Bulletin of Marine Science, 61(2): 343–375, 1997.
- Friedrich von Hellwald - The standard natural history, Volume 1, The Standard Natural History, Elliott Coues, Editors John Sterling Kingsley, Elliott Coues. Publisher S.E. Cassino and company, 1884, Pages 171–172.