Common sand dollar

Language English

Onglets

Description

Distinguishing features

As its name suggests, the common sand dollar resembles a large coin and doesn’t have the five arms that other echinoderms have. Its body is shaped like a flat disc and it ranges in colour from reddish to purple-brown. The topside is darker than the underside.

The test, the name given to the sand dollar’s rigid skeleton, has small, symmetric perforations shaped like petals. The test is also covered in miniscule spines, which sand dollars use to move about and even burrow into the sand.

The test also has small holes through which protrude little tube-feet, similar to those of starfish and sea urchins. It is these tube-feet that allow a sand dollar to move about.

In addition to its small spines, the surface of its body is covered in small pincer-like structures that it uses to clean its surface and rid itself of any parasites.

This marine animal’s mouth is located in the middle of the underside of its body. It has five small teeth that point toward the center.

Reproduction

There are few differences between males and females. Both the eggs and sperm are released into the water. The larvae swim freely through the water and plankton and then, after several successive metamorphoses, attach themselves to the bottom, develop their test and finally become true sand dollars.

Diet

Sand dollars move across the sea bottom, where they feed on algae and bits of organic matter. Sand dollars can also eat small grains of sand and digest any attached microorganisms (diatoms and other algae).

To obtain their food, sand dollars have to rake and scrape the seabed with their five large, triangular teeth that encircle their mouths like a crown. Sand dollars’ teeth are constantly being worn down. To compensate for that problem, their teeth never stop growing.

Predators

This marine species has few known predators. Its thin body and hard shell make it relatively unappetizing. However, the ocean pout enjoys a good sand dollar meal, just like certain starfish. In addition, crabs, plaice, cod, haddock and seagulls won’t hesitate to attack if the opportunity arises.

Large waves and strong winds can also kill sand dollars by pushing them onto the shore. Once there, the sun’s heat can dry them out.

Habitat

This is a circumpolar species, meaning that sand dollars live in all ocean waters surrounding the North Pole. They are found in Alaska, British Columbia, Siberia, Japan and Europe. On North America’s Atlantic coast, sand dollars can be found from the Arctic to New Jersey, in the U.S. They are common in the Gulf of St. Lawrence, all the way up to Tadoussac.

Sand dollars live in sandy areas bordering intertidal zones, the stretches spanning between the high-tide and low-tide lines.

Ecology, behaviour

Like most other echinoderms (starfish, sea urchins and sea cucumbers), sand dollars use their ambulacral (tube) feet to move about.

To dig into the ground, sand dollars use their spines, which are covered in small hair-like cilia. The back-and-forth movement of these cilia allows sand dollars to burrow into the sand and to direct any organic waste in their immediate surroundings toward their mouths.

It takes sand dollars about 10 minutes to burrow fully into the sand. In natural settings, they can dig up to 10 meters down!

French name

Dollar des sables

Scientific name

Echinarachnius parma

Phylum

Echinodermata

Class

Echinoidea

Order

Clypeasteroida

Family

Echinarachniidea

Size

Diameter: from 5 to 10 cm

Weight

From 10 to 20 g

Life span

13 years in nature

Status

Non-threatened species

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