''Ophiactis savignyi'' is a

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

brittle star Brittle stars, serpent stars, or ophiuroids (; ; referring to the serpent-like arms of the brittle star) are echinoderms in the class Ophiuroidea, closely related to starfish. They crawl across the sea floor using their flexible arms for locomot ...

in the

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

Ophiactidae Ophiactidae are a family of brittle stars. Genera The following genera are recognised by the World Register of Marine Species The World Register of Marine Species (WoRMS) is a taxonomic database that aims to provide an authoritative and com ...

, commonly known as Savigny's brittle star or the little brittle star. It occurs in the tropical and subtropical parts of all the world's oceans and is thought to be the brittle star with the most widespread distribution. It was first described by the German zoologists

Johannes Peter Müller Johannes Peter Müller (14 July 1801 – 28 April 1858) was a German physiologist, comparative anatomist, ichthyologist, and herpetologist, known not only for his discoveries but also for his ability to synthesize knowledge. The paramesonephri ...

and Franz Hermann Troschel in 1842. The specific name honours the French zoologist Marie Jules César Savigny.

Description

The disc of ''O. savignyi'' is up to in diameter. The aboral (upper) surface is covered by large overlapping scales and bears a scattering of spines, especially round the edges of the disc. The (usually) six arms are long, slender and tapering, and are composed of many segments with joints between them. Each segment bears five or six thorny spines. The aboral surface of the disc is a pale greenish-brown colour and the large, triangular radial shields, close to the origins of the arms, are contrastingly darker. The oral (under) surface is cream-coloured.

Distribution and habitat

''O. savignyi'' has a near

cosmopolitan distribution In biogeography, a cosmopolitan distribution is the range of a taxon that extends across most or all of the surface of the Earth, in appropriate habitats; most cosmopolitan species are known to be highly adaptable to a range of climatic and en ...

in warm seas. It is present in the western Indo-Pacific region, the eastern Pacific Ocean, and on both sides of the Atlantic Ocean. The populations in the Pacific and the Atlantic Oceans were only united when the

Panama Canal The Panama Canal () is an artificial waterway in Panama that connects the Caribbean Sea with the Pacific Ocean. It cuts across the narrowest point of the Isthmus of Panama, and is a Channel (geography), conduit for maritime trade between th ...

was cut across the

Isthmus of Panama The Isthmus of Panama, historically known as the Isthmus of Darien, is the narrow strip of land that lies between the Caribbean Sea and the Pacific Ocean, linking North America, North and South America. The country of Panama is located on the i ...

in 1914. This brittle star occurs from the intertidal zone down to about . It is found in all the zones of reefs, in

mangrove A mangrove is a shrub or tree that grows mainly in coastal saline water, saline or brackish water. Mangroves grow in an equatorial climate, typically along coastlines and tidal rivers. They have particular adaptations to take in extra oxygen a ...

habitats, in

seagrass meadow A seagrass meadow or seagrass bed is an underwater ecosystem formed by seagrasses. Seagrasses are marine (saltwater) plants found in shallow coastal waters and in the brackish waters of estuaries. Seagrasses are flowering plants with stems and ...

s, among

seaweed Seaweed, or macroalgae, refers to thousands of species of macroscopic, multicellular, marine algae. The term includes some types of ''Rhodophyta'' (red), '' Phaeophyta'' (brown) and ''Chlorophyta'' (green) macroalgae. Seaweed species such as ...

s and in contaminated waters, and is often found living inside

sponge Sponges or sea sponges are primarily marine invertebrates of the animal phylum Porifera (; meaning 'pore bearer'), a basal clade and a sister taxon of the diploblasts. They are sessile filter feeders that are bound to the seabed, and a ...

s, possibly as a

commensal Commensalism is a long-term biological interaction (symbiosis) in which members of one species gain benefits while those of the other species neither benefit nor are harmed. This is in contrast with mutualism, in which both organisms benefit f ...

Ecology

''Ophiactis savignyi'' is a deposit feeder and a

scavenger Scavengers are animals that consume Corpse decomposition, dead organisms that have died from causes other than predation or have been killed by other predators. While scavenging generally refers to carnivores feeding on carrion, it is also a he ...

, feeding on the

detritus In biology, detritus ( or ) is organic matter made up of the decomposition, decomposing remains of organisms and plants, and also of feces. Detritus usually hosts communities of microorganisms that colonize and decomposition, decompose (Reminera ...

that accumulates on the sea bed. It raises the tips of its arms to detect food particles, rolls any nutritious items into a ball and moves them to the mouth, manipulating them by means of the

tube feet Tube or tubes may refer to: * Tube (2003 film), ''Tube'' (2003 film), a 2003 Korean film * "Tubes" (Peter Dale), performer on the Soccer AM#Tubes, Soccer AM television show * Tube (band), a Japanese rock band * Tube & Berger, the alias of dance/e ...

. Examination of the stomach contents showed the remains of

bryozoa Bryozoa (also known as the Polyzoa, Ectoprocta or commonly as moss animals) are a phylum of simple, aquatic animal, aquatic invertebrate animals, nearly all living in sedentary Colony (biology), colonies. Typically about long, they have a spe ...

ns,

foraminifera Foraminifera ( ; Latin for "hole bearers"; informally called "forams") are unicellular organism, single-celled organisms, members of a phylum or class (biology), class of Rhizarian protists characterized by streaming granular Ectoplasm (cell bio ...

ns and

gastropod Gastropods (), commonly known as slugs and snails, belong to a large Taxonomy (biology), taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, freshwater, and fro ...

among the large quantities of detritus and grains of sand that this brittle star had ingested. Individual ''O. savignyi'' are either male or female, and they can reproduce either sexually or asexually. Sexual reproduction involves the liberation of sperm and eggs into the sea and the development and eventual settlement of

plankton Plankton are the diverse collection of organisms that drift in Hydrosphere, water (or atmosphere, air) but are unable to actively propel themselves against ocean current, currents (or wind). The individual organisms constituting plankton are ca ...

larva A larva (; : larvae ) is a distinct juvenile form many animals undergo before metamorphosis into their next life stage. Animals with indirect development such as insects, some arachnids, amphibians, or cnidarians typically have a larval phase ...

e. Asexual reproduction is by fragmentation, each portion being the same sex as its parent. Small, immature individuals (disc diameter under ) usually have six arms and can split themselves in two and then regenerate the missing parts of the disc and arms, often ending up with five arms. Most larger individuals have five arms and can also undergo fragmentation. The larger males do so more often than do the females, and this may account for the fact that there is an excess of males in the population. After splitting, the brittle star may still be able to reproduce sexually but some fragments of the disc may have no

gonad A gonad, sex gland, or reproductive gland is a Heterocrine gland, mixed gland and sex organ that produces the gametes and sex hormones of an organism. Female reproductive cells are egg cells, and male reproductive cells are sperm. The male gon ...

s and thus be unable to

spawn Spawn or spawning may refer to: * Spawning, the eggs and sperm of aquatic animals Arts, entertainment and media * Spawn (character), a fictional character in the comic series of the same name and in the associated franchise ** ''Spawn: Armageddon' ...

until regeneration is complete. In Taiwan, mature gametes occur at any time from March to December, but most of the population of ''O. savignyi'' spawn during May and June. Fission takes place at any time of year but mostly occurs between July and December. Sampling the brittle stars throughout the year resulted in finding that 48% of the individuals inspected were in the process of regeneration. The sex ratio in this locality is twenty-four males for every one female. In Hawaii, this brittle star is often to be found living in association with a sponge such as '' Lissodendoryx schmidti'' (previously ''Damiriana hawaiiana''). Up to twenty individuals can be found clumped together in cavities in the base of the sponge, the area being so filled with the slime secreted by the sponge that the brittle stars can hardly move their arms. These brittle stars often seem to have broken or partly regenerated arms. It is not clear how they enter the sponge, nor how they feed or reproduce.

References

{{Taxonbar, from=Q2766693 Ophiactidae Echinoderms of the Atlantic Ocean Echinoderms of Brazil Echinoderms of the Indian Ocean Echinoderms of the Pacific Ocean Echinoderms described in 1842