Sand Dollar
Closeup on a Sand Dollar
Scientific classification
Kingdom: Animalia Phylum: Echinodermata Class: Echinoidea Subclass: Euechinoidea Superorder: Gnathostomata Order: Clypeasteroida
Suborders
Clypeasterina Laganina Rotulina Scutellina

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. Download high resolution version (1024x768, 117 KB)Sand dollar closeup Caption: Sand Dollar by erikdungan: Sand dollar on the shore. ... Scientific classification or biological classification is how biologists group and categorize extinct and living species of organisms. ... Phyla Porifera (sponges) Ctenophora (comb jellies) Cnidaria Placozoa Bilateria  Acoelomorpha  Orthonectida  Rhombozoa  Myxozoa  Superphylum Deuterostomia     Chordata (vertebrates, etc. ... Classes Asteroidea Concentricycloidea Crinoidea Echinoidea Holothuroidea Ophiuroidea Echinoderms (Echinodermata) is a phylum of marine animals found in the ocean at all depths. ... Slate pencil urchin (cidaroid) Group of black, long-spined Caribbean sea urchins, Diadema antillarum (Philippi) Sea urchin roe. ... In biology, the skeleton or skeletal system is the biological system providing support in living organisms. ... Phyla Porifera (sponges) Ctenophora (comb jellies) Cnidaria Placozoa Bilateria  Acoelomorpha  Orthonectida  Rhombozoa  Myxozoa  Superphylum Deuterostomia     Chordata (vertebrates, etc. ... A sun is the star at the center of a solar system. ...

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. Subclasses Euechinoidea Superorder Atelostomata Order Cassiduloida Order Spatangoida (heart urchins) Superorder Diadematacea Order Diadematoida Order Echinothurioida Order Pedinoida Superorder Echinacea Order Arbacioida Order Echinoida Order Phymosomatoida Order Salenioida Order Temnopleuroida Superorder Gnathostomata Order Clypeasteroida (sand dollars) Order Holectypoida Perischoechinoidea Order Cidaroida (pencil urchins) Slate pencil urchin (cidaroid) Group of black... Closeup on a Sand Dollar A number of sand dollars on a seabed The common sand dollar is the skeleton or test of a marine animal. ... Subclasses Euechinoidea Superorder Atelostomata Order Cassiduloida Order Spatangoida (heart urchins) Superorder Diadematacea Order Diadematoida Order Echinothurioida Order Pedinoida Superorder Echinacea Order Arbacioida Order Echinoida Order Phymosomatoida Order Salenioida Order Temnopleuroida Superorder Gnathostomata Order Clypeasteroida (sand dollars) Order Holectypoida Perischoechinoidea Order Cidaroida (pencil urchins) Slate pencil urchin (cidaroid) Group of black... A pore, in general, is some form of opening, usually very small. ...

A number of sand dollars on a seabed

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. Sand dollars Caption: 137. ... Sand dollars Caption: 137. ... cross-section of two cilia, showing 9+2 structure A cilium (plural cilia) is a fine projection from a eukaryotic cell that constantly beats in one direction. ... Photomontage of plankton organisms Plankton are the weakly swimming but mostly drifting small organisms that inhabit the water column of the ocean, seas, and bodies of freshwater. ...

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. Ocean (from Okeanos, a Greek god of sea and water; Greek ωκεανός) covers almost three quarters (71%) of the surface of the Earth. ... Reproduction is perhaps most commonly used in the context of biological reproduction and sex: Sexual reproduction is a biological process by which organisms create descendants through the combination of genetic material. ... Gametes (in Greek: γαμέτες) —also known as sex cells, germ cells, or spores—are the specialized cells that come together during fertilization (conception) in organisms that reproduce sexually. ... A larva (Latin; plural larvae) is a juvenile form of animal with indirect development, undergoing metamorphosis (for example, insects or amphibians). ...

The name "sand dollar" is a reference to the round, flat shape of the skeleton, which is similar to a large coin.

Live sand dollar on a beach

Underside of same live sand dollar

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

External Links:

• The Sand Dollar Legend - The history of the sand dollar and a legend about them.
• The Common Sand Dollar by Cheryl Page
• GREAT WEBSITE from Ask a Scientist