Animal Diversity Web

Geographic Range

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)

• Biogeographic Regions
• atlantic ocean
  • native

Habitat

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.

Elevated water temperatures at low tides can kill some individuals. (Hendler, et al., 1995; Meinkoth, 1981)

• Habitat Regions
• saltwater or marine

• Aquatic Biomes
• reef
• coastal

• Range depth

  24 (high) m

  78.74 (high) ft

Physical Description

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)

• Other Physical Features
• ectothermic
• heterothermic
• radial symmetry

• Range length

  150 (high) mm

  5.91 (high) in

Development

• Development - Life Cycle
• metamorphosis

Reproduction

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)

• Key Reproductive Features
• seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual
• fertilization
  • external
• oviparous

• Parental Investment
• no parental involvement

Behavior

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)

• Key Behaviors
• nocturnal
• sessile
• motile
• sedentary
• territorial

Food Habits

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)

• Primary Diet
• carnivore
  • piscivore
  • eats eggs
• omnivore
• planktivore
• detritivore

• Animal Foods
• fish
• eggs

• Plant Foods
• algae

• Other Foods
• detritus

• Foraging Behavior
• filter-feeding

Predation

Ophiocoma echinata is eaten by some fish. (Hendler, et al., 1995)

Economic Importance for Humans: Positive

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)

Economic Importance for Humans: Negative

The spiny brittle star has no negative economic effects on humans.

Conservation Status

• IUCN Red List

  No special status

• US Federal List

  No special status

• CITES

  No special status

Other Comments

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)

Contributors

Renee Sherman Mulcrone (editor).

Aubrey Buckert (author), Southwestern University, Stephanie Fabritius (editor), Southwestern University.

References

Banister, K., A. Campbell. 1985. The Encyclopedia of Aquatic Life. New York: Facts on File, Inc..

Barnes, R. 1980. Invertebrate Zoology. Philadelphia: Holt, Rinehart and Winston.

Buchsbaum, R. 1960. The Lower Animals Living Invertebrates of the World. Garden City: Boubleday and Company, Inc..

Duque, C., J. Rojas, S. Zea, A. Roccatagliata, M. Maier, A. Seldes. 1997. Main Sterols from the Ophiuroids Ophiocoma echinata, Ophiocoma wendtii, Ophioplocus januarii and Ophionotus victoriae . Biochemical Systematics adn Ecology, 25: 775-778. Accessed August 22, 2003 at http://www.sciencedirect.com/science?_ob=ArticleURL&_aset=W-WA-A-A-B-MsSAYZA-UUW-AUZADVYUYD-WUACAYAUA-B-U&_rdoc=2&_fmt=summary&_udi=B6T4R-3S12BWD-7&_coverDate=12%2F31%2F1997&_cdi=4981&_orig=search&_st=13&_sort=d&view=c&_acct=C000007678&_version=1&_urlVersion=0&_userid=99318&md5=d4bd07905d889b859068a470c4d02a68.

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.