''Ophiocomina nigra'', commonly known as the black brittle star or black serpent star, 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 ...

of marine

invertebrate Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate ...

in the

order Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of d ...

Ophiurida The Ophiurida are an order of echinoderms within the class Ophiuroidea. It includes the vast majority of living brittle stars. Characteristics Ophiurida have bursae for respiration and excretion, and dorsal and ventral arm shields are present a ...

. It occurs in the north-eastern Atlantic Ocean, the North Sea and the Mediterranean Sea.

Description

''O. nigra'' is a large brittle star with five narrow arms up to 125mm long and a quite distinct central disc which is up to 25mm wide. The general colour is black or varying shades of brown, but pale coloured specimens occasionally occur. The upper surface of the disc is covered with fine granules which obscure the plates which cover the surface. On the underside the granules are restricted to the outer portion and the plates are visible towards the central mouth. This is surrounded by the feeding apparatus known as Aristotle's lantern with five toothed jaws each with oval jaw plates.Black Brittle Star (''Ophiocomina nigra'')
Marine Species Identification Portal. Retrieved 2011-08-31. There is a comb-like arrangement of spines down either side of the arms giving them a bristly appearance.Black brittlestar: ''Ophiocomina nigra''

Marine Life Information Network The Marine Life Information Network (MarLIN) is an information system for marine biodiversity for Great Britain and Ireland Ireland ( ; ga, Éire ; Ulster Scots dialect, Ulster-Scots: ) is an island in the Atlantic Ocean, North Atlantic O ...

. Retrieved 2011-08-31. On the upper side, each arm segment is covered by a broad plate with 5 to 7 spines. On the underside there are tube feet but these have no suckers.

Distribution and habitat

''O. nigra'' occurs in the eastern Atlantic Ocean from

Norway Norway, officially the Kingdom of Norway, is a Nordic country in Northern Europe, the mainland territory of which comprises the western and northernmost portion of the Scandinavian Peninsula. The remote Arctic island of Jan Mayen and t ...

south to the

Azores ) , motto =( en, "Rather die free than subjected in peace") , anthem= ( en, "Anthem of the Azores") , image_map=Locator_map_of_Azores_in_EU.svg , map_alt=Location of the Azores within the European Union , map_caption=Location of the Azores wi ...

, and also the

North Sea The North Sea lies between Great Britain, Norway, Denmark, Germany, the Netherlands and Belgium. An epeiric sea on the European continental shelf, it connects to the Atlantic Ocean through the English Channel in the south and the Norwegian S ...

and the

Mediterranean Sea The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western and Southern Europe and Anatolia, on the south by North Africa, and on the ea ...

. It is found on rocks, boulders and gravel in the neritic zone down to about one hundred metres but is occasionally found at greater depths. It is tolerant of low salinity levels.

Biology

''O. nigra'' is a

predator Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill th ...

scavenger Scavengers are animals that consume 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 herbivorous feeding b ...

and

filter feeder Filter feeders are a sub-group of suspension feeding animals that feed by straining suspended matter and food particles from water, typically by passing the water over a specialized filtering structure. Some animals that use this method of feedin ...

. It catches pieces of organic detritus and small invertebrate prey with its arms and thrusts them into its mouth. It can scavenge from carcases or graze on algal films.Ecology of Bed-Forming Brittlestars
Retrieved 2011-08-31. As a suspension feeder, it raises one or more arms into the current of water flowing past. There is a net of mucous threads among the spines on the arms which trap plankton and other organic floating matter. These are then rolled into boluses and transported to the mouth by ciliary currents and the tube feet. Breeding of ''O. nigra'' takes place in June in the

Firth of Clyde The Firth of Clyde is the mouth of the River Clyde. It is located on the west coast of Scotland and constitutes the deepest coastal waters in the British Isles (it is 164 metres deep at its deepest). The firth is sheltered from the Atlantic ...

Scotland Scotland (, ) is a country that is part of the United Kingdom. Covering the northern third of the island of Great Britain, mainland Scotland has a border with England to the southeast and is otherwise surrounded by the Atlantic Ocean to the ...

. A large female is often found in association with a smaller male, which clings above or below her. Fertilisation however takes place in the

water column A water column is a conceptual column of water from the surface of a sea, river or lake to the bottom sediment.Munson, B.H., Axler, R., Hagley C., Host G., Merrick G., Richards C. (2004).Glossary. ''Water on the Web''. University of Minnesota-D ...

and is a chance meeting of two

gamete A gamete (; , ultimately ) is a haploid cell that fuses with another haploid cell during fertilization in organisms that reproduce sexually. Gametes are an organism's reproductive cells, also referred to as sex cells. In species that produce t ...

s. The larvae are

plankton Plankton are the diverse collection of organisms found in Hydrosphere, water (or atmosphere, air) that are unable to propel themselves against a Ocean current, current (or wind). The individual organisms constituting plankton are called plankt ...

ic and settle out after several months. The species seems to be slow-growing and long-lived, not becoming mature before the age of three or four years.

Ecology

''O. nigra'' is often found living in association with another brittle star, ''

Ophiothrix fragilis ''Ophiothrix fragilis'' is a species of brittle star in the order Ophiurida. It is found around the coasts of western Europe and is known in Britain as the common brittle star. It is also found along the coast of South Africa where it is known ...

''. Numerous individuals of these two species sometimes form dense

communities A community is a Level of analysis, social unit (a group of living things) with commonality such as place (geography), place, Norm (social), norms, religion, values, Convention (norm), customs, or Identity (social science), identity. Communiti ...

with hundreds of brittle stars per square metre. These beds may extend several hundred square metres over sandy and pebbly sediment on the sea floor and contain millions of brittle stars. These can be either ''O. nigra'' or ''O. fragilis'', or a mixed community of the two. The vast social agglomerations can be advantageous in enabling the brittle stars to filter feed in fast moving currents which would otherwise sweep them away.''Ophiothrix fragilis'' and/or ''Ophiocomina nigra'' brittlestar beds on sublittoral mixed sediment
Joint Nature Conservation Committee. Retrieved 2011-08-31. Often the bed consists of adults and newly settled juveniles, with intermediate sized individuals living elsewhere. Other

echinoderm An echinoderm () is any member of the phylum Echinodermata (). The adults are recognisable by their (usually five-point) radial symmetry, and include starfish, brittle stars, sea urchins, sand dollars, and sea cucumbers, as well as the sea ...

s likely to be in the same vicinity (and enjoying the feast) are the

predatory Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill th ...

starfish, ''

Asterias rubens The common starfish, common sea star or sugar starfish (''Asterias rubens'') is the most common and familiar starfish in the north-east Atlantic. Belonging to the family Asteriidae, it has five arms and usually grows to between 10–30 ...

'', ''

Luidia ciliaris ''Luidia ciliaris'', the seven-armed sea star, is a species of sea star (starfish) in the family Luidiidae. It is found in the eastern Atlantic Ocean and the Mediterranean Sea. Description ''L. ciliaris'' is an orangeish-brown colour and has s ...

'' and ''

Crossaster papposus The common sunstar is a species of sea star (aka starfish) belonging to the family Solasteridae. It is found in the northern parts of both the Atlantic and the Pacific Oceans. Distribution The common sunstar is distributed from the Arctic dow ...

'' and the

sea urchin Sea urchins () are spiny, globular echinoderms in the class Echinoidea. About 950 species of sea urchin live on the seabed of every ocean and inhabit every depth zone from the intertidal seashore down to . The spherical, hard shells (tests) of ...

s, ''

Echinus esculentus ''Echinus esculentus'', the European edible sea urchin or common sea urchin, is a species of marine invertebrate in the Echinidae family. It is found in coastal areas of western Europe down to a depth of . It is considered "Near threatened" in t ...

'' and ''

Psammechinus miliaris ''Psammechinus miliaris'' is a species of sea urchin in the family Parechinidae. It is sometimes known as the green sea urchin or shore sea urchin. It is found in shallow areas of the eastern Atlantic Ocean and the North Sea. Description ''P. ...

''. Also present are likely to be the crabs '' Cancer pagurus'', '' Necora puber'' and '' Liocarcinus spp.'', and the hermit crab, ''

Pagurus bernhardus ''Pagurus bernhardus'' is the common marine hermit crab of Europe's Atlantic coasts. It is sometimes referred to as the common hermit crab or soldier crab. Its carapace reaches long, and is found in both rocky and sandy areas, from the Arctic wa ...

''. On rocky outcrops among the seething mass of brittle stars the soft coral, '' Alcyonium digitatum'', the hydroid, '' Nemertesia antennina'' and the

sea anemone Sea anemones are a group of predation, predatory marine invertebrates of the order (biology), order Actiniaria. Because of their colourful appearance, they are named after the ''Anemone'', a terrestrial flowering plant. Sea anemones are classifi ...

, '' Metridium senile'', are often found. Another sea anemone, ''

Urticina felina The dahlia anemone (''Urticina felina'') is a sea anemone found in the north Atlantic Ocean, the North Sea and the Baltic Sea. Its colour is variable, from deep red to brown or purplish, with green spots and darker tentacles. Dahlia anemones liv ...

'', may be semi-buried in the sediment and surrounded by an area clear of brittle stars.Warner, G.F., 1971. On the ecology of a dense bed of the brittle-star ''Ophiothrix fragilis''. Journal of the Marine Biological Association of the United Kingdom, 51: 267-282.

References

External links

* {{Taxonbar, from=Q2342919 Ophiocomidae Animals described in 1789