''Ophiactis savignyi'' is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

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 la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

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 compr ...

, 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 and

Franz Hermann Troschel Franz Hermann Troschel (10 October 1810 – 6 November 1882) was a German zoologist born in Spandau. He studied mathematics and natural history at the University of Berlin, where he was awarded his doctorate in 1834.Beolens, Bo; Watkins, Michael; ...

in 1842. The specific name honours the French zoologist

Marie Jules César Savigny Marie Jules César Lelorgne de Savigny (; 5 April 1777 – 5 October 1851) was a French zoologist. Savigny was born at Provins. In 1798 he travelled to Egypt with the Emperor Napoleon as part of the French scientific expedition to that country ...

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 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 ( es, Canal de Panamá, link=no) is an artificial waterway in Panama that connects the Atlantic Ocean with the Pacific Ocean and divides North and South America. The canal cuts across the Isthmus of Panama and is a condui ...

was cut across the Isthmus of Panama 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 in coastal saline or brackish water. The term is also used for tropical coastal vegetation consisting of such species. Mangroves are taxonomically diverse, as a result of convergent evolution in severa ...

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

sponge Sponges, the members of the phylum Porifera (; meaning 'pore bearer'), are a basal animal clade as a sister of the diploblasts. They are multicellular organisms that have bodies full of pores and channels allowing water to circulate throug ...

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 fro ...

Ecology

''Ophiactis savignyi'' is a deposit feeder and a scavenger, feeding on the detritus 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 feet (technically podia) are small active tubular projections on the oral face of an echinoderm, whether the arms of a starfish, or the undersides of sea urchins, sand dollars and sea cucumbers; they are more discreet though present on br ...

. 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 invertebrate animals, nearly all living in sedentary colonies. Typically about long, they have a special feeding structure called a ...

ns,

foraminifera Foraminifera (; Latin for "hole bearers"; informally called "forams") are single-celled organisms, members of a phylum or class of amoeboid protists characterized by streaming granular ectoplasm for catching food and other uses; and commonly ...

ns and gastropod 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 found in water (or air) that are unable to propel themselves against a current (or wind). The individual organisms constituting plankton are called plankters. In the ocean, they provide a crucia ...

larva A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. ...

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 gonads and thus be unable to

spawn Spawn or spawning may refer to: * Spawn (biology), 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: ...

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 Animals described in 1842