The name 'sand dollar' refers to its round, flat shape that resembles a large coin. The decorative, fragile disk found in the sand is, in reality, the skeleton or ‘test’ of a marine animal related to sea urchins and sea stars. The live creature is of a greenish or maroon-coloured suit of moveable, velvety spines that cover the entire shell. Spines on the upper half of the sand dollar’s body serve as gills.
Sand Dollars' Habitat is the Sandy Ocean Floor
Sand dollars live on top of or just beneath the sandy surface or muddy areas of the sea floor at thirty to forty-foot depths. The flattened underside of the amazing creature has spines that let it slowly creep through the sand or burrow into it. Microscopic, hair-like projections on the spines combined with mucous coating, move food to the mouth opening at the center of the grooves on the shell’s underside. Its food consists of crustacean larvae, algae, and organic particles that float by or end up in the sandy bottom.
On the ocean bottom, sand dollars are frequently found together. Their preference for soft-bottomed areas pertains to their reproduction habits. The separate sexes release cells into a water column and through several stages the free-swimming larvae develop. Sand dollars sometimes congregate in groups of thousands.
In quiet waters they are tilted up on their edge waiting for floating food items. In rough waters they lay flat or burrow in. To fight fast-moving currents, the adults grow heavier skeletons while the young sand dollars swallow heavy grains of sand to weight themselves down.
Sand Dollars Have Few Predators
Few animals bother the sand dollars because of their tiny edible parts and hard skeleton but they are eaten by starfish, snails, and one animal found to enjoy them on occasion is the thick-lipped, eel-like ocean pout.
Collecting Sand Dollars
Sand dollars are abundant on the sandy bottom of deeper waters around the world. The shell of the sand dollar (Echinarachnius parma) shown in the attached photograph was found in Nova Scotia, Canada.
Any one interested in collecting the shells should look on sandy beaches at the time of receding tide. Shells that are dredged up by increased wave action caused by heavy storms are often plentiful. When you find them in the sand, the dead sand dollars will be missing their velvety covering and will be slightly bleached or greenish in appearance from exposure to the sun.
Broken open, the skeleton or ‘test’ reveals many loose, hard white pieces. They are the sand dollar’s teeth. In legends many people refer to the teeth as doves because of their shape.
Before collecting live specimens or shells, ensure that this will not put stress on the local ecosystem.
Reference: Gosner, Kenneth L., Guide to Identification of Marine and Estuarine Invertebrates: Cape Hatteras to the Bay of Fundy1971 by John Wiley & Sons, Inc.
Kathleen Airdrie - Kathleen has thirty years' freelance writing experience covering history, biographical profiles, environmental and social issues
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