Sand dollar
The sand dollar is a round, flat echinoderm closely related to sea urchins, starfish, and sea cucumbers, and is often found along sandy shores and tidal flats in warm ocean waters, particularly around Central and South America. With over 250 species in the order Clypeasteroida, sand dollars typically measure between 2 to 4 inches in diameter. Their distinctive flat bodies feature five markings that resemble a star, and they are often found as empty shells on beaches. Living sand dollars possess velvety spines and fine cilia that aid in burrowing and capturing food. They feed by using their cilia to trap tiny particles in the sand, which are then transported to their mouths through grooves on their undersides. Sand dollars reproduce through a spawning process, releasing eggs and sperm into the water, where fertilization occurs. The lifespan of a sand dollar ranges from 6 to 10 years, and they are preyed upon by various marine animals, including snails and sea stars. Their unique shape and habitat make them a fascinating subject for coastal exploration.
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Sand dollar
The sand dollar is named for its habitat and likeness to a silver dollar. A silver dollar is a round, silver coin that equals one dollar. The sand dollar is closely related to sea urchins, starfish, and sea cucumbers. They are sometimes called sea cookies, sand cakes, cake urchins, or snapper biscuits.
Kingdom: Animalia
Phylum: Echinodermata
Class: Echinoidea
Order: Clypeasteroida
Family: Various (see below)
Genus: Various (see below)
Species: Various (see below)
There are more than 250 species of sand dollars in the order Clypeasteroida. They are typically found buried in the sand and mud below the low tide mark along sandy shores and tidal flats. They are warm water creatures that lives in the warm ocean waters around Central and South America. Sometimes, it is found as far north as North Carolina.
Growing to an average diameter of 2 to 4 inches (5 to 10 centimeters), the sand dollar is a round echinoderm, or spiny-skinned animal. A diameter is a measurement of the distance from one side of a circle to the other side. Round or radially symmetrical animals are described according to their diameter, or the distance from one side of their bodies to the other. A radially symmetrical animal is one whose body extends in a circle from a central axis, or main point. The starfish is a radially symmetric animal. The sand dollar, a close relative of the starfish, is radially symmetrical internally beneath its round test, or shell.
Unlike many other echinoderms, the sand dollar is flat, instead of spherical like a ball. On its flat body are five markings that resemble a star. Humans usually find the empty tests, or shells, of sand dollars. At that point, it is hard and does not have any hair or spines, but when the sand dollar is living within its test it has many short, velvety spines and thin, fine hair, or cilia. These hairs and spines stick out from holes in the sand dollar's test. The spines typically help the sand dollar burrow into the sand, and the cilia help the sand dollar catch food.
The sand dollar gathers food by beating its cilia in the wet sand and tidal pools. Tiny particles get stuck in the cilia and the mucus produced by the spines. These particles are then passed into one of the five long grooves on the bottom of the sand dollar. These grooves pass food from the cilia to the sand dollar's mouth.
The sand dollar is often preyed upon by sea snails (Syrinx aruanus), starry flounder (Platichthys stellatus), California sheephead (Semicossyphus pulcher), and the giant pink sea stars (Pisaster brevispinus). Some snails can drill holes into the hard test of the sand dollar and suck out its softer body parts.
Like other echinoderms, the sand dollar mates in the spring and summer. The male and female sand dollars release their sperm and eggs into the water for fertilization. This system of reproduction is known as spawning and is practiced by many species of fish. In the water, the eggs are fertilized by sperm and develop into tiny sand dollar larvae. Many sand dollar eggs are carried out to sea before being fertilized by the male’s sperm. Sand dollar larvae drift along the water’s surface for a few weeks before settling on the seabed and maturing into adult sand dollars.
The life span of the sand dollar is 6 to 10 years.
Species include:
Common sand dollar Echinarachnius parma
Eccentric sand dollar Dendraster excentricus
Green urchin Echinocyamus pusillus
Japanese sea biscuit Clypeaster japonicus
Reticulated sea biscuit Clypeaster reticulatus
Six-holed keyhole urchin Leodia sexiesperforata
West African sand dollar Heliophora orbicularis
Bibliography
"Everything You Need to Know About the Sand Dollar." Sand Dollar Shelling, sanddollarshelling.com/seashells/everything-you-need-to-know-about-the-sand-dollar. Accessed 15 Apr. 2024.
"Sand Dollar." Monterey Bay Aquarium, www.montereybayaquarium.org/animals/animals-a-to-z/sand-dollar. Accessed 15 Apr. 2024.
"Sea Wonder: Sand Dollar." National Marine Sanctuary Foundation, marinesanctuary.org/blog/sea-wonder-sand-dollar. Accessed 15 Apr. 2024.