The life cycles of keyhole urchins are complex and pass through several stages of metamorphosis. After the eggs have been fertilized they will develop into swimming larvae that are bilaterally symmetrical. These swimming larvae are covered with cilia, drift about the sea water as plankton for four to six weeks, and feed on tiny organisms until they metamorphosize into young keyhole urchins that will grow into adults on the ocean floor. The young keyhole urchins eat sand and store it in their gut to weigh them down while developing into adults. Adult keyhole urchins are radially symmetrical. Like all Echinoderms, keyhole urchins are coelomates and deuterostomates. (Fotheringham, 1989; Hyman, 1995; McHenry, 1998)
Keyhole urchins reproduce sexually by external fertilization. Millions of eggs and sperm are released into the water where fertilization occurs. They are also capable of regeneration of spines and areas of their test. (Fotheringham, 1989; McHenry, 1998)
There is no parental investment post-spawning.
The average lifespan of (McHenry, 1998)is four years, but they have been known to survive for up to ten years.
Keyhole urchins are free-living social animals. They live in large groups which can serve as means of protection and successful reproduction, since fertilization is external. Living in large groups is thought to be influenced by food availablity. In contrast to other echinoderms with arms, the keyhole urchin can only right itself when turned over by burying itself vertically and then falling over right side up. (Bullough, 1950; Fotheringham, 1989; Hyman, 1995; McHenry, 1998)
Keyhole urchins sense the surrounding environment, light, and temperature by touch through the many sensory cells that are located on the epdermis. These cells are also used to communicate socially. (Hyman, 1995; McHenry, 1998)
Keyhole urchins are omnivorous and pull food particles from the sand with their tube feet. The food particles are then guided toward the mouth by cilia and mucous. Foods eaten include microorganisms, algae, marine plants and shellfish. (Fotheringham, 1989; Hyman, 1994; The Assateague Naturalist, 2001)
Keyhole urchins passively defend themselves. The tough skeleton and spines serve as defense mechanisms. They also burrow under the sand to hide. (Fotheringham, 1989; Gosner, 1978; McHenry, 1998; The Assateague Naturalist, 2001)
There is no known positive importance for humans.
There is no known negative importance for humans.
Keyhole urchins are most commonly called sand dollars. They are mostly found washed ashore on beaches and are widely collected by beachcombers and bleach white once they die. Sand dollars have also been used by Christians as a symbol of their beliefs. (Fotheringham, 1989; The Assateague Naturalist, 2001)
Renee Sherman Mulcrone (editor).
Lauren Sweeten (author), Southwestern University, Stephanie Fabritius (editor), Southwestern University.
the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.
uses smells or other chemicals to communicate
the nearshore aquatic habitats near a coast, or shoreline.
animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature
fertilization takes place outside the female's body
union of egg and spermatozoan
having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.
the area of shoreline influenced mainly by the tides, between the highest and lowest reaches of the tide. An aquatic habitat.
seaweed. Algae that are large and photosynthetic.
A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.
having the capacity to move from one place to another.
the area in which the animal is naturally found, the region in which it is endemic.
an animal that mainly eats all kinds of things, including plants and animals
a form of body symmetry in which the parts of an animal are arranged concentrically around a central oral/aboral axis and more than one imaginary plane through this axis results in halves that are mirror-images of each other. Examples are cnidarians (Phylum Cnidaria, jellyfish, anemones, and corals).
mainly lives in oceans, seas, or other bodies of salt water.
breeding is confined to a particular season
reproduction that includes combining the genetic contribution of two individuals, a male and a female
associates with others of its species; forms social groups.
uses touch to communicate
that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).
the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.
uses sight to communicate
Bullough, W. 1950. Practical Invertebrate Anatomy. London: Macmillan & Co..
Fotheringham, N. 1989. Beachcomber's Guide to Gulf Coast Marine Life. Houston, TX: Gulf Publishing Company.
Fox, R. 2001. "Mellita quinquiesperforata" (On-line). Accessed 12/14/04 at http://www.lander.edu/rsfox/310mellitaLab.html.
Gosner, K. 1978. A Field Guide to the Atlantic Seashore. Boston: Houghton Mifflin Company.
Hyman, L. 1995. Echinoderm. Pp. "505-506" in Collier's Encyclopedia Vol.8. New York: P.F. Collier.
Hyman, L. 1994. Sand Dollar. Pp. "392-393" in Collier's Encyclopedia Vol. 20. New York: P.F. Collier.
McHenry, R. 1998. Echinoderms. Pp. "857-865" in The New Encyclopedia Britannica Vol.17 15th Edition. Chicago, IL: Encyclopedia Britannica Inc..
Meinkoth, N. 1981. The Audubon Society Field Guide to North American Seashore Creatures. New York: Chanticleer Press.
The Assateague Naturalist, 2001. "Keyhole Sand Dollar" (On-line). Accessed 12/14/04 at http://www.assateague.com/sand-dol.html.