Ophiactis savignyi

Geographic Range

Ophiactis savignyi can be found in tropical marine habitats around the globe. Humans may have contributed to the dispersal of O. savignyi, especially in the western and eastern populations around the Isthmus of Panama. The species was separated by the isthmus until humans opened it with the Panama Canal. Ophiactis savignyi is found in the Pacific, the Atlantic Oceans, the Persian Gulf, and the Mediterranean Sea. Its ranges also include the northern, western, and eastern coasts of South America, Hawaii, French Polynesia, the Gulf of Mexico, the Caribbean, and the south-eastern and south-western coasts of North America. The brittle star is also along the coast of Australia and Southeast Asia extending up into China's eastern coast. This species is considered the most common brittle star in the world. (Chao and Tsai, 1995; McKeton and Wood, 2006; Roy and Sponer, 2001; Roy and Sponer, 2002; Smithsonian Marine Station at Fort Pierce, 2010; Stohr and Hansson, 2009)

Habitat

Ophiactis savignyi is benthic and resides inshore, on continental shelves, and continental slopes. This brittle star shelters itself in various subtropical marine and tropical marine habitats, including rubble, algae, corals, sponges, reefs, mangrove areas, ship hulls, and sea grasses like turtle grass. Ophiactis savignyi is more frequent on sponges than algae. This species can inhabit sponges in densities up to 1,892 individuals per 100 grams of dried sponge; 3,000 individuals per liter have also been reported. The density of O. savignyi depends on space and food available. One species of sponge inhabited by this brittle star is Tedania ignis; an inhabited algae species is Sargassum cymosum. (Boffi, 1972; Chao and Tsai, 1995; Hendler, et al., 1995; McGovern, 2002a; McGovern, 2002b; McKeton and Wood, 2006; Mladenov and Emson, 1988; Smithsonian Marine Station at Fort Pierce, 2010)

  • Range depth
    1 to 518 m
    3.28 to 1699.48 ft
  • Average depth
    259 m
    849.74 ft

Physical Description

Ophiactis savignyi is radially symmetric as an adult, and is generally found with six arms, but can be found with 1-7 arms. Individuals with fewer arms are in the process of regeneration. Like other ophiuroids, O. savignyi has arms that are sharply demarcated from the central disk. The arms are jointed and flexible and are usually variegated with intermittent dark and light markings. The animal's color ranges from mixes of green, brown, white, yellow, and cream. The oral surface is lighter than the aboral surface. Australian members of this species have a brown disc with bright yellow arms, but the species is usually green or blue. The disc of the animal is 3.8-5 mm and darkly pigmented with rough-tipped spines on top of the disc. The arms of the animal range from 16.3 mm-20 mm and have small, rough spines running along them. The oral surface of the central disc contains one to three oral papilliae that are flat and scaly. In O. savignyi, fission causes species to have a variable number of arms; specimens that recently split typically have three large arms and three small regenerating ones. (Hendler, et al., 1995; McKeton and Wood, 2006; Smithsonian Marine Station at Fort Pierce, 2010; Stohr and Hansson, 2009)

Sexual reproduction results in planktonic ophiopluteus larvae that have bilateral symmetry. They are v-shaped and have a crystalline skeleton with curving ciliated bands for feeding. Ophiopluteus larvae are free swimming until they metamorphose into adults. (Hendler, et al., 1995; Schoener, 1972)

  • Sexual Dimorphism
  • sexes alike

Development

The newly fertilized eggs of O. savignyi turn into ophiopluteus larvae. The larvae have a crystalline skeleton, are bilateral, and free-swimming. The exact amount of time before metamorphosis into a radial, benthic adult is unknown, but it is estimated to be a month. Individuals produced by fission regenerate into two adult organisms. (Boffi, 1972; McGovern, 2002a; McGovern, 2002b; Roy and Sponer, 2001; Schoener, 1972)

Reproduction

Sexual reproduction by O. savignyi involves broadcast spawning. Each sex scatters its gametes in the water column. During sexual reproduction gametes from different colonies presumably mix. Sexual reproduction is followed by asexual reproduction via fission. The majority of individuals lose the ability to reproduce sexually after splitting. Sexual reproduction, in summer and fall, is usually followed by asexual reproduction. The separation of these two breeding modes may be because after splitting, O. savignyi must regenerate its lost limbs, which takes away from its ability to produce eggs and sperm. In both sexes the gametes of one or both of the newly divided brittle stars are reabsorbed. When O. savignyi reaches a large enough size, at least a 3.0 mm disc, it begins to spawn sexually. (Boffi, 1972; Chao and Tsai, 1995; McGovern, 2002a; McGovern, 2002b; Mladenov and Emson, 1988; Schoener, 1972)

Ophiactis savignyi reproduces either through asexual splitting or sexual broadcast spawning. Asexual reproduction occurs by voluntary splitting down the organism's central disc, producing two halves, which regenerate into two functioning organisms; this and predation accounts for odd number of limbs found in some individuals. In O. savignyi simultaneous asexual and sexual reproduction is also known to occur, but mature gonads are usually reabsorbed in one or both freshly split clones, making simultaneous sexual reproduction unlikely. (Boffi, 1972; Chao and Tsai, 1995; McGovern, 2002a; McGovern, 2002b; McKeton and Wood, 2006)

Sexual maturity of O. savignyi appears to depend on size. Ophiactis savignyi displays a difference in sex ratio that results in a higher proportion of males than females. This difference may be due to a greater investment in gonad mass by females. Males are more likely to retain their ability to reproduce after splitting than females, which may be the cause of the male biased sex ratio. Sexual spawning may result in long-distance colonization of sponges and algae by brittle stars and would also account for the unusual sex ratio; a single organism can generate an entire colony. In Harrington Sound, a sponge colony was found with an all male sex ratio that supports this hypothesis. (Chao and Tsai, 1995; McGovern, 2002a; McGovern, 2002b; Mladenov and Emson, 1988)

  • Breeding interval
    Asexual and sexual year round, but sexual more frequent late summer to fall.

Ophiactis savignyi does not have any parental investment. When large enough the organism reproduces sexually. Immature and mature organisms reproduce by splitting with both halves being autonomous. (Boffi, 1972; Hendler, et al., 1995; McGovern, 2002a; McKeton and Wood, 2006; Morgado and Tanaka, 2001; Schoener, 1972)

  • Parental Investment
  • no parental involvement

Lifespan/Longevity

No information on the lifespan was found. (Boffi, 1972; Chao and Tsai, 1995; McGovern, 2002a; McGovern, 2002b; McKeton and Wood, 2006; Roy and Sponer, 2001)

Behavior

This brittle star forms colonies made of asexually produced clones, and the occasional sexually acquired recruit. Information on the locomotion specifically of O. savignyi was not found. Other ophiuroids move by pulling themselves along with their flexible arms. They move in any direction across the substrate and do not favor a particular arm. An interesting discrepancy in damage-release reaction time exists between populations of this species on algae and sponges. The populations studied were close to each other. During sexual reproduction gametes from different colonies presumably mix. The expected result from this interbreeding is a similar response signal across all colonies, but this is not supported by the data. This has led to the hypothesis that Ophiactis savignyi may be exhibiting learned behavior. More research is needed to support this claim. (Majer, et al., 2009; McGovern, 2002a; McKeton and Wood, 2006; Mladenov and Emson, 1988)

Communication and Perception

Ophiactis savignyi, like other ophiuroids, perceives the environment by chemosensors in its tube feet. This brittle star is also able to detect very dilute concentrations of amino acids, and vitamins, which allows it to detect food and predators. Ophiactis savignyi responds to damage-release alarm signals. A divergence in response time to chemical alarm signals occurs between algae and sponge dwelling individuals of the species. Individuals dwelling in an algae habitat respond to conspecific (interspecies) and heterospecific (among different species) signals. Sponge dwelling individuals have little response to heterospecific signals. Sponge dwelling O. savignyi are better protected from predators and do not have as much environmental pressure as their algae dwelling members. This species also exhibits negative phototaxis (move away from light), and senses light from light-sensitive cells in skeletal plates within its dermis. (Hendler, et al., 1995; Majer, et al., 2009; McGovern, 2002a)

Food Habits

Ophiactis savignyi is detritophagous, i.e., it feeds mainly on small particles of detritus. The stomach typically contains foraminiferans, bryozoans, organic detritus, and small gastropods. This brittle star is a suspension feeder using its tube feet to catch small particles and moving them toward its mouth. Ophiactis savignyi is also characterized as a deposit feeder, cleaning the outer surface of its habitat and filtering food from the water. A large individual suspension feeds by raising its arms into the water column. Ophiactis savignyi will also situate itself at the base of the excurrent pore of a sponge to collect food particles. (Hendler, et al., 1995; McKeton and Wood, 2006)

  • Animal Foods
  • mollusks
  • aquatic crustaceans
  • other marine invertebrates
  • zooplankton

Predation

A defense mechanism of O. savignyi is its use of autonomy (casting off of limbs) when escaping predators. It also is capable of regenerating them. Negative phototaxis and damage-release alarm signals are also evolved characteristics to escape predators. A fish may bite the brittle star into smaller pieces before consuming it, so the ability to lose and regenerate limbs is an advantage. This species is prey to crabs and shrimp. (Hendler, et al., 1995; McKeton and Wood, 2006)

Ecosystem Roles

Ophiactis savignyi dominates sponge habitats and competes with other brittle stars for space. In the Caribbean it inhabits at least ten species of sponges. This brittle star also inhabits various algae. Numbers are greater in sponges than in algal turf, probably because sponges provide a better refuge against predators. Other than providing food for species of fish, shrimp, and crab, the species at times occludes the excurrent siphon of sponges, which is potentially harmful. Ophiactis savignyi acts as a detritivore and recycles dead plankton, bacteria, small crustaceans, and invertebrates.

Algae that O. savignyi inhabit include Hypnea species. Sponges that O. savignyi inhabit include Haliclona species, Tedania ignis, Scopalina ruetzleri, and Amphimedon viridis. (Boffi, 1972; Chao and Tsai, 1995; Hendler, et al., 1995; McGovern, 2002b; Mladenov and Emson, 1988)

Economic Importance for Humans: Positive

Ophiactis savignyi has no significant positive impact on humans. (; McKeton and Wood, 2006)

Economic Importance for Humans: Negative

This species has no negative impact on humans or economic importance to them. (; McGovern, 2002b; McKeton and Wood, 2006)

Conservation Status

The tropical brittle star, O. savignyi, is not considered endangered. This species has a global distribution in tropical and subtropical regions, and is very abundant. (Chao and Tsai, 1995; Hendler, et al., 1995; McGovern, 2002a; McGovern, 2002b; McKeton and Wood, 2006; Mladenov and Emson, 1988; Stohr and Hansson, 2009)

Contributors

Jason Haas (author), University of Michigan-Ann Arbor, Phil Myers (editor), University of Michigan-Ann Arbor, Renee Mulcrone (editor), Special Projects.

Glossary

Atlantic Ocean

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.

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Australian

Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

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Ethiopian

living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.

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Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

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Neotropical

living in the southern part of the New World. In other words, Central and South America.

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Pacific Ocean

body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.

Palearctic

living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

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asexual

reproduction that is not sexual; that is, reproduction that does not include recombining the genotypes of two parents

benthic

Referring to an animal that lives on or near the bottom of a body of water. Also an aquatic biome consisting of the ocean bottom below the pelagic and coastal zones. Bottom habitats in the very deepest oceans (below 9000 m) are sometimes referred to as the abyssal zone. see also oceanic vent.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

biodegradation

helps break down and decompose dead plants and/or animals

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

colonial

used loosely to describe any group of organisms living together or in close proximity to each other - for example nesting shorebirds that live in large colonies. More specifically refers to a group of organisms in which members act as specialized subunits (a continuous, modular society) - as in clonal organisms.

cosmopolitan

having a worldwide distribution. Found on all continents (except maybe Antarctica) and in all biogeographic provinces; or in all the major oceans (Atlantic, Indian, and Pacific.

detritivore

an animal that mainly eats decomposed plants and/or animals

detritus

particles of organic material from dead and decomposing organisms. Detritus is the result of the activity of decomposers (organisms that decompose organic material).

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

external fertilization

fertilization takes place outside the female's body

fertilization

union of egg and spermatozoan

filter-feeding

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.

herbivore

An animal that eats mainly plants or parts of plants.

heterothermic

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.

metamorphosis

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.

molluscivore

eats mollusks, members of Phylum Mollusca

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

oriental

found in the oriental region of the world. In other words, India and southeast Asia.

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pheromones

chemicals released into air or water that are detected by and responded to by other animals of the same species

phytoplankton

photosynthetic or plant constituent of plankton; mainly unicellular algae. (Compare to zooplankton.)

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

radial symmetry

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).

reef

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.

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

tactile

uses touch to communicate

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

visual

uses sight to communicate

year-round breeding

breeding takes place throughout the year

zooplankton

animal constituent of plankton; mainly small crustaceans and fish larvae. (Compare to phytoplankton.)

References

Boffi, E. 1972. Ecological aspects of ophiuroids from the phytal of S. W. Atlantic Ocean warm waters. Marine Biology, 15: 316-328.

Chao, S., C. Tsai. 1995. Reproduction and population dynamics of the fissiparous brittle star Ophiactis savignyi (Echinodermata: Ophiuroidea. Marine Biology, 124: 77-83.

Hendler, G., J. Miller, D. Pawson, P. Kier. 1995. Sea Stars, Sea Urchins, and Allies Echinoderms of Florida and the Caribbean. Washington and London: Smithsonian Institution Press.

Majer, A., J. Trigo, L. Duarte. 2009. Evidence of an alarm signal in Ophiuroidea (Echinodermata). Marine Biodiversity Records, 2: e102.

McGovern, T. 2002. Patterns of sexual and asexual reproduction in the brittle star Ophiactis savignyi in the Florida Keys. Marine Ecology Progress Series, 230: 119-126.

McGovern, T. 2002. Sex-ratio bias and clonal reproduction in the brittlestar Ophiactis savignyi. Evolution, 56 (3): 511-517.

McKeton, K., J. Wood. 2006. "Marine Invertebrates of Bermuda" (On-line). Little brittle star (Ophiactis savignyi). Accessed April 27, 2011 at http://www.thecephalopodpage.org/MarineInvertebrateZoology/Ophiactissavignyi.html.

Mladenov, P., R. Emson. 1988. Density, size structure and reproductive characteristics of fissiparous brittle stars in algae and sponges: evidence for interpopulational variation in levels of sexual and asexual reproduction. Marine Ecology Progress Series, 42: 181-194.

Morgado, E., M. Tanaka. 2001. The macrofauna associated with the bryozoan Schizoporella errata (Walters) in southeastern Brazil. Scientia Marina, 65 (3): 173-181.

Roy, M., R. Sponer. 2002. Evidence of a human-mediated invasion of the tropical western Atlantic by the ‘world’s most common brittlestar’. Proceedings of the Royal Society - Biological Sciences, 269: 1017-1023. Accessed April 23, 2011 at http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1690993/.

Roy, M., R. Sponer. 2001. The recent evolutionary history of Ophiactis savignyi (Echinodermata; Ophiuroidea). Pp. 307-311 in M Barker, ed. Echinoderms 2000: proceedings of the 10th international conference, Dunedin, Vol. 1st edition. Netherlands: Aa Balkema. Accessed April 23, 2011 at http://books.google.com/books?id=NEog_WHJ5HcC&pg=PA307&lpg=PA307&dq=Ophiactis+savignyi&source=bl&ots=QMXwQgcU4X&sig=PMPeVAuf6Ew17GClRIZ-_CL78gk&hl=en&ei=K7t5S437JI2KnQe9l_GnCQ&sa=X&oi=book_result&ct=result&resnum=4&ved=0CBAQ6AEwAzgK#v=onepage&q=&f=false.

Schoener, A. 1972. Fecundity and possible mode of development of some deep-sea ophiuroids. Limnology and Oceanography, 17 (2): 193-199.

Smithsonian Marine Station at Fort Pierce, 2010. "Field Guide to the Indian River Lagoon, Florida Savigny's Brittle Star Ophiactis savignyi" (On-line). Smithsonian Marine Station at Fort Pierce. Accessed May 02, 2011 at http://www.sms.si.edu/IRLFieldGuide/Ophiac_savign.htm.

Stohr, S., H. Hansson. 2009. "Ophiactis savignyi (Müller & Troschel, 1842)" (On-line). World Register of Marine Species. Accessed April 23, 2011 at http://www.marinespecies.eu/aphia.php?p=taxdetails&id=125122.