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Pacific Sand Dollar

Dendraster excentricus

Pacific sand dollars are an invertebrate member of the Echinodermata phylum. They are similar to a flattened sea urchin with a calcium carbonate exoskeleton also known as a test, however, they are flat, disk shaped instead of spherical. They range from Alaska to Baja Mexico. Pacific sand dollars are unique in their suspension feeding method, being the only sand dollar that digs into the sand to establish a vertical position. They live in large colonies on sandy bottoms in the low intertidal zone with moderate water movement at depths of 4—90 meters (13—295 feet). The colonies, or beds, position themselves upright parallel with the water flow to maximize food capture. Through their diet of algae, larval crustaceans, and detritus, they aid in filtering these items from the ocean floor. In areas of high current flow, they will ingest sand to provide ballast to hold their vertical position. In the wild, their lifespan can be up to 15 years. Age can be determined by counting the rings on the test. Intact sand dollar skeletons are prized finds by beach visitors.

sand dollars partially buried in the sand

Credit: Aquarium of the Pacific / Robin Riggs

SPECIES IN DETAIL

Pacific Sand Dollar

Dendraster excentricus

CONSERVATION STATUS: Safe for Now

CLIMATE CHANGE: Not Applicable

At the Aquarium

They may be viewed in Southern California/Baja Gallery at the Redondo Submarine Canyon exhibit.

Geographic Distribution

The Pacific sand dollar is found along the Eastern Pacific coastline from southern Alaska to Baja Mexico.

Habitat

They range from southern Alaska to Baja Mexico and live at depths from 4—90 meters (13—295 feet). They choose to stay on the sandy sea floor with mild to moderate water movement. Juveniles are found closer to shore and move to greater depths as they age.

Physical Characteristics

Named due to their resemblance to silver dollars, they develop a flat disk shaped calcium carbonate exoskeleton referred to as a test. Live sand dollars are pale gray-lavender to purple black in color . The test has a distinctive leaf-like pattern on its upside known as a petaloid. Tube-like feet used for feeding, respiration, and mobility are located along the petaloid. The test is covered in cilia which captures food from the current flow around the sand dollar. The mouth is located on the underside along with 5 structures known as doves. Doves are long slits in the test and include teeth and jaws for feeding. Their age can be determined by counting the rings on the upside of the test.

Size

They average 10 centimeters (4 inches). The size can vary based on localized conditions.

Diet

Pacific sand dollars are unique in the species as they use suspension feeding; they bury their anterior end into the sand and collect food with cilice that covers their body as the current passes around their body. They position themselves in colonies parallel to the current to maximize feeding. Their primary prey is algae, larval crustaceans and detritus.

Reproduction

Sand dollars broadcast spawn from July to August. This method is highly efficient given their high density colony lifestyle. Sexual maturity is reached at an average of four years of age. There is no noticeable difference between males and females. Fertilized eggs are yellow and coated in a protective jelly that protects them from being eaten by predators. The eggs quickly develop into larvae which go through several stages of development. The complete development process from fertilization to the juvenile phase takes approximately eighteen days.

Behavior

During the juvenile phase, the sand dollar uses the tube feet in the petaloid for movement, upon adulthood they use their spines for propulsion. Burrowing into the sandy bottom they rotate their body to an incline position aligned parallel with the current for feeding and reproduction. They are often found organized in large colonies. Scientists believe their colonies are organized to increase water movement around the sand dollars to increase food flow. Small cilice which cover their body and capture food particles and move them to the mouth.

Adaptation

Unique among the sand dollar species, Pacific sand dollars have an off-center profile that allows for the suspension feeding process. Sand dollar larvae may clone themselves when exposed to predator stimulus to increase the likelihood of their survival. They organize themselves in inclined positions in their colony to aid in feeding and reproduction.

Longevity

Their average lifespan in the wild is fifteen years.

Conservation

Pacific sand dollars are currently not evaluated (NE) by ICUN. Recent studies of ocean acidification caused by increased carbon dioxide in the atmosphere have shown to have a negative impact on the species. Lower pH levels have shown to reduce the ability of species to develop calcium carbonate shells or exoskeletons, and at these reduced levels can dissolve them. In addition, the reproduction levels of Pacific Sand Dollars have shown to decrease with higher acidification.

Special Notes

Juvenile Pacific sand dollars will ingest sand to act as a ballast to aid in keeping their bodies upright in stronger currents. Their age can be determined by counting the rings on the test. The Pacific sand dollar is the only sand dollar species that can elevate itself in the sand to use suspension feeding. Complete sand dollar skeletons are highly prized by beach visitors!

SPECIES IN DETAIL | Print full entry

Pacific Sand Dollar

Dendraster excentricus

CONSERVATION STATUS: Safe for Now

CLIMATE CHANGE: Not Applicable

They may be viewed in Southern California/Baja Gallery at the Redondo Submarine Canyon exhibit.

The Pacific sand dollar is found along the Eastern Pacific coastline from southern Alaska to Baja Mexico.

They range from southern Alaska to Baja Mexico and live at depths from 4—90 meters (13—295 feet). They choose to stay on the sandy sea floor with mild to moderate water movement. Juveniles are found closer to shore and move to greater depths as they age.

Named due to their resemblance to silver dollars, they develop a flat disk shaped calcium carbonate exoskeleton referred to as a test. Live sand dollars are pale gray-lavender to purple black in color . The test has a distinctive leaf-like pattern on its upside known as a petaloid. Tube-like feet used for feeding, respiration, and mobility are located along the petaloid. The test is covered in cilia which captures food from the current flow around the sand dollar. The mouth is located on the underside along with 5 structures known as doves. Doves are long slits in the test and include teeth and jaws for feeding. Their age can be determined by counting the rings on the upside of the test.

They average 10 centimeters (4 inches). The size can vary based on localized conditions.

Pacific sand dollars are unique in the species as they use suspension feeding; they bury their anterior end into the sand and collect food with cilice that covers their body as the current passes around their body. They position themselves in colonies parallel to the current to maximize feeding. Their primary prey is algae, larval crustaceans and detritus.

Sand dollars broadcast spawn from July to August. This method is highly efficient given their high density colony lifestyle. Sexual maturity is reached at an average of four years of age. There is no noticeable difference between males and females. Fertilized eggs are yellow and coated in a protective jelly that protects them from being eaten by predators. The eggs quickly develop into larvae which go through several stages of development. The complete development process from fertilization to the juvenile phase takes approximately eighteen days.

During the juvenile phase, the sand dollar uses the tube feet in the petaloid for movement, upon adulthood they use their spines for propulsion. Burrowing into the sandy bottom they rotate their body to an incline position aligned parallel with the current for feeding and reproduction. They are often found organized in large colonies. Scientists believe their colonies are organized to increase water movement around the sand dollars to increase food flow. Small cilice which cover their body and capture food particles and move them to the mouth.

Unique among the sand dollar species, Pacific sand dollars have an off-center profile that allows for the suspension feeding process. Sand dollar larvae may clone themselves when exposed to predator stimulus to increase the likelihood of their survival. They organize themselves in inclined positions in their colony to aid in feeding and reproduction.

Their average lifespan in the wild is fifteen years.

Pacific sand dollars are currently not evaluated (NE) by ICUN. Recent studies of ocean acidification caused by increased carbon dioxide in the atmosphere have shown to have a negative impact on the species. Lower pH levels have shown to reduce the ability of species to develop calcium carbonate shells or exoskeletons, and at these reduced levels can dissolve them. In addition, the reproduction levels of Pacific Sand Dollars have shown to decrease with higher acidification.

Juvenile Pacific sand dollars will ingest sand to act as a ballast to aid in keeping their bodies upright in stronger currents. Their age can be determined by counting the rings on the test. The Pacific sand dollar is the only sand dollar species that can elevate itself in the sand to use suspension feeding. Complete sand dollar skeletons are highly prized by beach visitors!