TAXONOMY
Kingdom: Animalia
Phylum: Echinodermata (“spiny-skinned” animals including sea stars, brittle stars, sea urchins, sand dollars, and sea cucumbers)
Class: Echinoidea (sea urchins and sand dollars)
Order: Clypeasteroida
Suborder: Scutellina
Family: Dendrasteridae
Genus/species: Dendraster excentricus
GENERAL CHARACTERISTICS: Closely related to sea urchins, except for a more flattened, silver-dollar skeleton (test).
The tube feet, characteristic of echinoderms, are used for locomotion, respiration, sensing the environment, grasping and transporting food particles to the centrally located mouth on the underside of the test, and attachment to the substrate. The anus is near the edge of the test.
Very short spines which are covered with tiny hair-like cilia are closely packed together on the surface which feels like velvet.
Diameter to 8 cm (3.2 inches).
DISTRIBUTION/HABITAT: Southeastern Alaska to Baja California. Found in subtidal to low intertidal zone on sandy or sandy-muddy substrates in cool water near the shore, but deep enough to avoid wave surge. Depth to 40 m (131 feet) but usually shallower.
DIET IN THE WILD: They are oriented flat or more often vertical with entire bed oriented the same way to catch phytoplankton detritus, diatoms, and plankton such as crab larvae and amphipods. They are captured by mucous-covered spines and pincers (pedicillariae). Food particles are then carried to the mouth in the center of the lower body surface by cilia on spines where it is broken up by jaws of a small aristotle’s lantern. The tube feet are also used for grasping and transporting food.
REPRODUCTION: Broadcast spawner. Sperm and eggs are released from separate individuals. After fertilization, free-swimming bilateral larvae form, which eventually change to radially symmetrical individuals that settle to a sandy or muddy substrate similar to sea urchins.
Longevity: averages 10 years.
PREDATORS: Fish, sea stars, crabs, humans.
CONSERVATION: IUCN; Not evaluated.
REMARKS: Cilia covered spines are used in wave-like motions for movement and burrowing. Tube feet away from the mouth are also used for locomotion.
Young sand dollars ingest large sand grains that act like a diver’s weight belt to help them maintain position.
The age a sand dollar can be determined by counting the growth rings on the plates of the exoskeleton.
References
U. of Michigan (ADW) Animal Diversity Web http://animaldiversity.ummz.umich.edu/accounts/Dendraster_excentricus/
Walla Walla University http://www.wallawalla.edu/academics/departments/biology/rosario/inverts/Echinodermata/Class%20Echinoidea/Dendraster_excentricus.html
Monterey Bay Aquarium http://www.montereybayaquarium.org/animal-guide/invertebrates/sand-dollar
Ron’s flickr https://www.flickr.com/photos/cas_docents/3289660142/in/set-72157608501343477
Ron’s WordPress shortlink http://wp.me/p1DZ4b-1mA
Ron's Critter of the Day 