A dollar? Is that Canadian or American?

Did you know that the sand dollar is basically just a squashed sea urchin? Well, they're related anyway. They are both members of a group of organisms called the Echinoderms. When alive, they are covered with a suit of moveable spines that encompass the entire shell, but they are much smaller than those we are familiar with when we see the spiky urchins. Like its close relative the sea urchin, the sand dollar has five sets of pores arranged in a petal pattern. The pores are used to move sea water into its internal water-vascular system, which allows for movement. They are able to kind of "squish" the water through this canal system and use the pressure generated to move their tiny "tube-feet".

One of our members, Colin Dean, was in Tribune Bay- Hornby island in Aug and took some photos of a sand dollar bed. His pictures are included in this overview of these cool aquatic coins.

Sand dollars live beyond mean low water on top of (or just beneath) the surface of sandy or muddy areas. The spines on the somewhat flattened underside of the animal allow it to burrow or to slowly creep through the sand. Fine, hair-like cilia cover the tiny spines. Tubefeet or podia that line the food grooves, move food to the mouth opening which is in the center of the star shaped grooves on the underside of the animal called the oral surface. Its food consists of plankton and organic particles that end up in the sandy bottom.

On the ocean bottom, sand dollars are often found in large groups. This is due in part to their preference of soft bottom areas, which are convenient for their reproduction. The sexes are separate and gametes are released into the water column and it's up to the currents to bring them together, there's a lot of luck involved. The free-swimming larvae metamorphose through several stages before the hard exoskeleton (called the test) begins to form, and they become bottom dwellers.

The name "sand dollar" is a reference to their round flat shape, which is similar to a large coin. Sand dollars usually eat tiny particles of food that float in the water. They hide by burying themselves under the sand. The term "sand dollar" can also refer to the skeleton or test left when a sand dollar dies. By the time the test washes up on the beach, it is usually missing its velvety covering of minute spines and has a somewhat bleached appearance due to its exposure to the sun.

Want more? Try these sites:

http://animaldiversity.ummz.umich.edu/site/accounts/information/Echinoidea.html

http://www.sdnhm.org/fieldguide/fossils/sanddollars.html

Last growth spurt on February 12, 2008