The spiny brittle star can be found along the eastern coastlines of Central and South America to Brazil, Florida, and the majority of the islands in the Caribbean Sea. (Hendler, et al., 1995; Meinkoth, 1981)
Spiny brittle stars occupy reefs and reef flats, particularly those abundant in rubble. The stars are also found in seagrass beds and mangroves, under rocks, and in old coral heads. They live in shallow intertidal waters with depths up to 24 meters.
One of the larger brittle stars, Ophiocoma echinata can measure up to 32 mm in disk diameter and 150 mm in arm length. The spiny brittle star shares the characteristic body plan of echinoderms, with 5 arms that are well defined from the central disk. The aboral, or top, side of the star is dark brown and sometimes mottled with lighter hues. The arms are usually banded in shades of brown and the oral, or bottom, surface is white in color. The central disk is granular and exhibits a scalloped border. The mouth is located on the oral surface and consists of 5 triangular jaws, each with a central column of teeth. The arms extend out from the muscular jaws and are covered by 4 rows of shields, or calcareous plates. Each arm joint has a vertical row of 4 spines on either side. The length of the spines decease towards the tip of the arm and the spine closest to the mouth is club-shaped. Unlike the asteroids (sea stars), brittle stars have no umbulacral groove and lack the suction apparatus on the podia of the oral surface on the arms. (Barnes, 1980; Hendler, et al., 1995; Meinkoth, 1981)
Spiny brittle stars have testes and ovaries consisting of clusters of gametes in sac-like cavities called bursae. An individual 22 mm in disk length can contain 888,000 eggs. Sexes are separate, however, no sex differences have evolved because no sex recognition is necessary in the spawning process. Fertilization is external. Spawning takes place at night when the predation pressure is lowered. The stars assume a pop-up postion with the central disk lifted above the substratum and release a stream of gametes, either oocytes or spermatozoa, from the bursal slits. The male and female gametes must meet midstream to form a zygote. The fertilized eggs develop into larvae and are moved by the ocean current. After a few weeks, metamorphosis is complete and the larvae become juvenile spiny brittle stars. (Barnes, 1980; Hendler, et al., 1995; Kaplan, 1982)
The spiny stars are cryptic and shun all light. During the day, they usually seek refuge in the darkest of shadows and under any type of rubble. Some have been reported to hide inside of sea sponges with only the tips of 2 or 3 arms extended to catch food particles passing by in the ocean current. The star can be found in densities of up to thirty individuals per square meter. The overlapping of the many arms of the stars forms a web that is far superior for catching food than what any star could do on its own. While the stars do not usually leave the protection of their shelter, aggressive interspecific competition over burrow space among other species of brittle stars has been reported. The star moves in a swimming or serpentine motion, which is why they are sometimes called the serpent stars. One or two arms drag in front of and behind the central disk while two on the side perform a rapid rowing motion that sends the star forward in leaps or jerks. The star shows no preference on which arms to use and can move in any direction. (Barnes, 1980; Hendler, et al., 1995; Meinkoth, 1981)
The spiny stars can regenerate arms if lost, but this may reduce energy reserves and reproductive output. (Pomory and Lawrence, 1999)
The spiny brittle star is primarily a deposit and filter feeder, although some of the stars have been reported as carnivorous. The arms of the stars move from side to side, curving upward to intercept detritus and plankton. The food particles are caught in mucous strands strung between the spines and are then moved down to the mouth by the podia. Larger material is swept to the mouth by a looping action of the lateral movement of the arms. The stars feed mainly on pieces of fleshy algae, but some have been known to feed on eggs from damselfish nesting sites. The species possess an incomplete digestive tract, with the mouth also functioning as the anus, which is very unusual for an echnioderm. Feeding is done predominantly at night when the risk of predation is greatly reduced. (Banister and Campbell, 1985; Barnes, 1980; Hendler, et al., 1995)
Brittle stars have in the past only affected humans by figuring into the diets of commercially important marine life such as crabs, shrimp, and fish. Recently scientists have been researching the symbiotic relationship with a bacteria that lives between the stars' protective cuticle and inner skin layer. These bacteria protect the star from infection when arms are broken off. This research has great potential for antibiotic drugs and treatment of human diseases. (Duque, et al., 1997)
The spiny brittle star has no negative economic effects on humans.
The brittle star owes its name to the particular habit of voluntarily breaking off arms and portions of the central disk. There are no reproductive or digestive organs located in the arms, and loss is relatively inconsequential. An arm boken at the central disk can regenerate completely in 10 months. Another interesting fact about the star is the changing of colors from day to night. The adults are much paler at night than during the day. (Hendler, et al., 1995)
Renee Sherman Mulcrone (editor).
Aubrey Buckert (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.
an animal that mainly eats meat
the nearshore aquatic habitats near a coast, or shoreline.
an animal that mainly eats decomposed plants and/or animals
particles of organic material from dead and decomposing organisms. Detritus is the result of the activity of decomposers (organisms that decompose organic material).
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
a method of feeding where small food particles are filtered from the surrounding water by various mechanisms. Used mainly by aquatic invertebrates, especially plankton, but also by baleen whales.
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.
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.
active during the night
an animal that mainly eats all kinds of things, including plants and animals
reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.
an animal that mainly eats fish
an animal that mainly eats plankton
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).
structure produced by the calcium carbonate skeletons of coral polyps (Class Anthozoa). Coral reefs are found in warm, shallow oceans with low nutrient availability. They form the basis for rich communities of other invertebrates, plants, fish, and protists. The polyps live only on the reef surface. Because they depend on symbiotic photosynthetic algae, zooxanthellae, they cannot live where light does not penetrate.
mainly lives in oceans, seas, or other bodies of salt water.
breeding is confined to a particular season
remains in the same area
non-motile; permanently attached at the base.
Attached to substratum and moving little or not at all. Synapomorphy of the Anthozoa
reproduction that includes combining the genetic contribution of two individuals, a male and a female
defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement
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Hendler, G., J. Miller, D. Pawson, P. Kier. 1995. Sea Stars, Sea Urchins, and Allies. Washington: Smithsonian Institution Press.
Kaplan, E. 1982. Coral Reefs of the Carribean and Florida. Boston: Houghton Mifflin.
Meinkoth, N. 1981. The Audubon Society Field Guide to North American Seashore Creatures. New York: Alfred A. Knopf, Inc..
Pomory, C., J. Lawrence. 1999. Effect of arm regeneration on energy storage and gonad production in Ophiocoma echinata (Echinodermata: Ophiuroidea). Marine Biology, 135: 57-63.
eNature.com, 2003. "Enature.com" (On-line). Spiny Brittle Star, Ophiocoma echinata. Accessed August 19, 2003 at http://www.enature.com/fieldguide/showSpeciesSH.asp?curGroupID=8&shapeID=1072&curPageNum=12&recnum=SC0077.