Ophiocomina nigra
Encyclopedia
Ophiocomina nigra, commonly
known as the black brittle star or black serpent star, is a species
of marine invertebrate
in the order
Ophiurida
. It occurs in the north-eastern Atlantic Ocean, the North Sea and the Mediterranean Sea.
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. There is a comb-like arrangement of spines down either side of the arms giving them a bristly appearance. 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.
south to the Azores
, and also the North Sea
and the Mediterranean Sea
. 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.
, scavenger
and filter feeder
. 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. 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
, Scotland
. 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 and is a chance meeting of two gamete
s. The larvae are plankton
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.
. Numerous individuals of these two species sometimes form dense communities
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. Often the bed consists of adults and newly settled juveniles, with intermediate sized individuals living elsewhere. Other echinoderm
s likely to be in the same vicinity (and enjoying the feast) are the predatory
starfish, Asterias rubens, Luidia ciliaris
and Crossaster papposus and the sea urchin
s, Echinus esculentus and Psammechinus miliaris
. Also present are likely to be the crabs Cancer pagurus, Necora puber and Liocarcinus spp.
, and the hermit crab, Pagurus bernhardus
. On rocky outcrops among the seething mass of brittle stars the soft coral, Alcyonium digitatum
, the hydroid
, Nemertesia antennina and the sea anemone
, Metridium senile
, are often found. Another sea anemone, Urticina felina, may be semi-buried in the sediment and surrounded by an area clear of brittle stars.
Common name
A common name of a taxon or organism is a name in general use within a community; it is often contrasted with the scientific name for the same organism...
known as the black brittle star or black serpent star, is a species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of marine invertebrate
Invertebrate
An invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...
in the order
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...
Ophiurida
Ophiurida
The Ophiurida are an order of echinoderms within the class Ophiuroidea. It includes the vast majority of living brittle stars.-Characteristics:The upper surface of the disk of Ophiurida is covered with scales....
. It occurs in the north-eastern Atlantic Ocean, the North Sea and the Mediterranean Sea.
Description
O. nigra is a large brittle starBrittle star
Brittle stars or ophiuroids are echinoderms in the class Ophiuroidea closely related to starfish. They crawl across the seafloor using their flexible arms for locomotion. The ophiuroids generally have five long slender, whip-like arms which may reach up to in length on the largest specimens...
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. There is a comb-like arrangement of spines down either side of the arms giving them a bristly appearance. 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 NorwayNorway
Norway , officially the Kingdom of Norway, is a Nordic unitary constitutional monarchy whose territory comprises the western portion of the Scandinavian Peninsula, Jan Mayen, and the Arctic archipelago of Svalbard and Bouvet Island. Norway has a total area of and a population of about 4.9 million...
south to the Azores
Azores
The Archipelago of the Azores is composed of nine volcanic islands situated in the middle of the North Atlantic Ocean, and is located about west from Lisbon and about east from the east coast of North America. The islands, and their economic exclusion zone, form the Autonomous Region of the...
, and also the North Sea
North Sea
In the southwest, beyond the Straits of Dover, the North Sea becomes the English Channel connecting to the Atlantic Ocean. In the east, it connects to the Baltic Sea via the Skagerrak and Kattegat, narrow straits that separate Denmark from Norway and Sweden respectively...
and the Mediterranean Sea
Mediterranean Sea
The Mediterranean Sea is a sea connected to the Atlantic Ocean surrounded by the Mediterranean region and almost completely enclosed by land: on the north by Anatolia and Europe, on the south by North Africa, and on the east by the Levant...
. It is found on rocks, boulders and gravel in the neritic zone
Neritic zone
The neritic zone, also called coastal waters, the coastal ocean or the sublittoral zone, is the part of the ocean extending from the low tide mark to the edge of the continental shelf, with a relatively shallow depth extending to about 200 meters...
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 predatorPredation
In ecology, predation describes a biological interaction where a predator feeds on its prey . Predators may or may not kill their prey prior to feeding on them, but the act of predation always results in the death of its prey and the eventual absorption of the prey's tissue through consumption...
, scavenger
Detritivore
Detritivores, also known as detritophages or detritus feeders or detritus eaters or saprophages, are heterotrophs that obtain nutrients by consuming detritus . By doing so, they contribute to decomposition and the nutrient cycles...
and filter feeder
Filter feeder
Filter feeders are 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 feeding are clams, krill, sponges, baleen whales, and many fish and some sharks. Some birds,...
. 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. 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
Firth of Clyde
The Firth of Clyde forms a large area of coastal water, sheltered from the Atlantic Ocean by the Kintyre peninsula which encloses the outer firth in Argyll and Ayrshire, Scotland. The Kilbrannan Sound is a large arm of the Firth of Clyde, separating the Kintyre Peninsula from the Isle of Arran.At...
, Scotland
Scotland
Scotland is a country that is part of the United Kingdom. Occupying the northern third of the island of Great Britain, it shares a border with England to the south and is bounded by the North Sea to the east, the Atlantic Ocean to the north and west, and the North Channel and Irish Sea 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 and is a chance meeting of two gamete
Gamete
A gamete is a cell that fuses with another cell during fertilization in organisms that reproduce sexually...
s. The larvae are plankton
Plankton
Plankton are any drifting organisms that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. That is, plankton are defined by their ecological niche rather than phylogenetic or taxonomic classification...
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 fragilisOphiothrix fragilis
Ophiothrix fragilis is a species of brittle star in the order Ophiurida. It is found around the coasts of northwestern Europe and is known in Britain as the common brittle star.-Description:...
. Numerous individuals of these two species sometimes form dense communities
Community (ecology)
In ecology, a community is an assemblage of two or more populations of different species occupying the same geographical area. The term community has a variety of uses...
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. Often the bed consists of adults and newly settled juveniles, with intermediate sized individuals living elsewhere. Other echinoderm
Echinoderm
Echinoderms are a phylum of marine animals. Echinoderms are found at every ocean depth, from the intertidal zone to the abyssal zone....
s likely to be in the same vicinity (and enjoying the feast) are the predatory
Predation
In ecology, predation describes a biological interaction where a predator feeds on its prey . Predators may or may not kill their prey prior to feeding on them, but the act of predation always results in the death of its prey and the eventual absorption of the prey's tissue through consumption...
starfish, Asterias rubens, Luidia ciliaris
Luidia ciliaris
Luidia ciliaris or the seven armed starfish is a species of starfish in the family Luidiidae. It is found in the eastern Atlantic Ocean and the Mediterranean Sea.-Description:...
and Crossaster papposus and the sea urchin
Sea urchin
Sea urchins or urchins are small, spiny, globular animals which, with their close kin, such as sand dollars, constitute the class Echinoidea of the echinoderm phylum. They inhabit all oceans. Their shell, or "test", is round and spiny, typically from across. Common colors include black and dull...
s, Echinus esculentus and Psammechinus miliaris
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:...
. Also present are likely to be the crabs Cancer pagurus, Necora puber and Liocarcinus spp.
Liocarcinus
Liocarcinus is a genus of crabs, which includes the flying crab, the vernal crab and several other swimming crabs. It includes 12 species :*Liocarcinus bolivari...
, and the hermit crab, Pagurus bernhardus
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. It is about long, and is found in both rocky and sandy areas, from the Arctic waters of Iceland, Svalbard and Russia as far south as southern...
. On rocky outcrops among the seething mass of brittle stars the soft coral, Alcyonium digitatum
Alcyonium digitatum
Alcyonium digitatum or dead man's fingers is a species of soft coral in the Alcyoniidae family. It is found around the coasts of the northern Atlantic Ocean.-Description:...
, the hydroid
Hydrozoa
Hydrozoa are a taxonomic class of very small, predatory animals which can be solitary or colonial and which mostly live in saltwater. A few genera within this class live in freshwater...
, Nemertesia antennina and the sea anemone
Sea anemone
Sea anemones are a group of water-dwelling, predatory animals of the order Actiniaria; they are named after the anemone, a terrestrial flower. Sea anemones are classified in the phylum Cnidaria, class Anthozoa, subclass Zoantharia. Anthozoa often have large polyps that allow for digestion of larger...
, Metridium senile
Metridium senile
Metridium senile, common name the plumose anemone or frilled anemone, is a species of sea anemone in the family Metridiidae. It is found in the seas off northwest Europe and the east and west coasts of North America.-Description:...
, are often found. Another sea anemone, Urticina felina, may be semi-buried in the sediment and surrounded by an area clear of brittle stars.