The Common Sand DollarEchinarachnius parma

By Katie Wallace

Classification of the Common Sand Dollar:

• Kingdom:• Phylum:• Class:• Order:• Family:• Genus:• Species:

AnimaliaEchinodermata

EchinoideaClypeasteroidaEchinarachniidaeEchinarachniusparma

HABITATIt isn’t uncommon to find dead sand dollars washed up on the main beach in Kouchibouguac National Park, New Brunswick.

General Characteristics

ADAPTATIONS

• Over time, sea urchins evolved into sand dollars, and went from being shaped like a ball, to flat and round.

• This adaptation was for burrowing purposes.

Sand dollars have what is called a “test”. It surrounds the sand dollar entirely and protects it from the elements. It is made up of very tiny spines and it may also be known as a shell.

There are tiny spikes that stick out on either side of the mouth. They prevent the sand dollar from being swept away by the current in the ocean, and they help it burrow in the sand.

• The mouth is located on the bottom of the sand dollar (the flat side). “Black spines "on the bottom of the sand dollar trap food that floats by, and “cilia” guide the food into the mouth. The food is then sent off to be digested.

• Sand dollars are unable to prey on other animals because its hard for them to move around. They are scavengers because they feed on detritus, which is dead, decaying matter. They sit on the seafloor waiting for food to go near the mouth. Sometimes they can get their body to a vertical position so that they can catch what is floating by them. Because this isn't easy for them to do, it doesn’t happen often.

Feeding Habits

Respiration and movement, and circulation all use the same system, called a “water vascular system”, to function. Sea water is pumped into their “tube-like” feet, which are connected to canals that travel throughout the sand dollar. These canals allow the sea water to travel through the body.

Respiration,Movement

and

Circulation

• Sand dollars don’t have gills!• In respiration, the oxygen from the

sea water in the canals is absorbed through the walls, rather than through gills.• This process is called diffusion.

Respiration

• Sand dollars move by contracting muscles in opposite directions

• This forces the sea water from the canals into the tube feet and back into the ocean, causing the sand dollar to lift off the sea floor.

Movement

They get into their vertical position for feeding by forcing the water out of one side of the sand dollar, causing half of it to lift, while the other half stays on the seafloor. Once it is completely vertical, it waits for food to come its way.

• Sand dollars have a very simple circulatory system.

• It is also controlled by the “water vascular system”, this means that its powered by the movement of water through the canals.

• Contracting muscles cause the water to continuously move throughout these canals

Circulation

• Sand dollars reproduce like sea urchins.• Depending on whether a sand dollar is female or male, it

releases its sperm/eggs into the water.• Not too long after the eggs are fertilized, they become

larvae, and float freely in the ocean until they begin the next stage of their life. Larvae are mobile, which means they don’t move themselves, they allow something else to move them.

• The larvae still has a long way to go before it becomes a fully grown sand dollar. There are still many more stages of the lifecycle before the adult stage.

Reproduction

PredatorsBecause of their hard, rigid “test”, few animals want to snack on them, predators include:• starfish• skates• snails

Works CitedAbles, J. 2000. “Echinarachnius parma”. Animal Diversity Web. Accessed November 7, 2011.

http://animaldiversity.ummz.umich.edu/site/accounts/information/Echinarachnius_parma.html“sand dollar”. The Columbia Electronic Encyclopedia. Copyright 1994, 2000-2006, on infoplease. Copyright

2000-2007 Pearson Education, publishing as infoplease. Accessed November 7, 2011.http://www.infoplease.com/ce6/sci/A0843401.html.

“Sand Dollar”. Last modified, December 16, 2010. CreationWiki. Accessed November 7, 2011. http://creationwiki.org/Sand_dollar.

“Intertidal zone”. Dictionary.com’s 21st Century Lexicon. Dictionary.com, LLC. Accessed November 7, 2011.http://dictionary.reference.com/browse/intertidal_zone.

“Sand Dollar”. Enchanted Learning. Accessed December 3, 2011.http://www.enchantedlearning.com/subjects/invertebrates/echinoderm/sanddollarprintout.shtml.

“sand Dollar”. Last modified November 30, 2011. Wikipedial.org. Accessed November 7, 2011. http://en.wikipedia.org/wiki/Sand_dollar.

“Water vascular system”. Last modified, December 31, 2011. Wikipedia.org. Accessed December 3rd, 2011.http://en.wikipedia.org/wiki/Water_vascular_system.