Sand dollar
|
|
| Sand Dollar | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
 Closeup on a Sand Dollar | ||||||||||||
| Scientific classification | ||||||||||||
| ||||||||||||
| Suborders | ||||||||||||
The common sand dollar is the skeleton or test of a marine animal. By the time the test washes up on the beach, it is missing its velvety covering of minute spines and has a somewhat bleached appearance due to its exposure to the sun.
Sand dollars are in the Echinoid class of marine animals. When alive, one species, Echinarachnius parma, is outfitted in a maroon-colored suit of moveable spines that encompass the entire shell. 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.
SandDollarsOnSeabed.JPG
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. These cilia, in combination with a mucous coating, move food to the mouth opening which is in the center of the star shaped grooves on the underside of the animal. The anus is also located on the bottom, near the edge. Its food consists of plankton and organic particles that end up in the sandy bottom.
On the ocean bottom, sand dollars are frequently found together. This is due in part to their preference of soft bottom areas, which are convenient for their reproduction. The sexes are separate and, as with most echinoids, gametes are released into the water column. The free-swimming larvae metamorphose through several stages before the test begins to form, and they become bottom dwellers.
The name "sand dollar" is a reference to the round, flat shape of the skeleton, which is similiar to a large coin.
References
- Gosner, Kenneth L., Guide to Identification of Marine and Estuarine Invertebrates; 1971 by John Wiley & Sons, Inc.
- Robbins, Sarah Fraser and Clarice Yentsch, The Sea Is All About Us; 1973 Harcourt Brace Jovanovich, Inc.
- Animal Diversity Web classification of Order Clypeasteroida (http://animaldiversity.ummz.umich.edu/site/accounts/classification/Clypeasteroida.html)
External Links:
- The Sand Dollar Legend (http://www3.ns.sympatico.ca/samson3/dollar.htm) - The history of the sand dollar and a legend about them.
- The Common Sand Dollar by Cheryl Page (http://octopus.gma.org/Tidings/sanddollar.html)
- GREAT WEBSITE from Ask a Scientist (http://oceanlink.island.net/ask/echino.html)de:Sanddollars