''Amphiura filiformis'' is a species of

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 locomo ...

belonging to the

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

Amphiuridae Amphiuridae (commonly called long-armed burrowing brittle stars or burrowing brittle stars) are a large family of brittle stars of the suborder Gnathophiurina. Some species are used to study echinoderm development (e.g. '' Amphipholis kochii'' an ...

. It is found on the seabed in the north east Atlantic Ocean and adjoining seas to a depth of . It digs itself a shallow burrow in the sand and waves its arms in the water above to suspension feed on

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 ...

Description

''Amphiura filiformis'' has a central disc up to in diameter and five slender arms up to long. The aboral (upper) side of the disc is covered in fine scales but there are none on the oral (under side). The general colour of this brittle star is greyish or reddish-brown and it is

bioluminescent Bioluminescence is the production and emission of light by living organisms. It is a form of chemiluminescence. Bioluminescence occurs widely in marine vertebrates and invertebrates, as well as in some Fungus, fungi, microorganisms including ...

, emitting a bluish light.

Distribution and habitat

''Amphiura filiformis'' is found in the north east Atlantic Ocean, 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 ...

, the

Irish Sea The Irish Sea or , gv, Y Keayn Yernagh, sco, Erse Sie, gd, Muir Èireann , Ulster-Scots: ''Airish Sea'', cy, Môr Iwerddon . is an extensive body of water that separates the islands of Ireland and Great Britain. It is linked to the Ce ...

, 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 ...

and the

Adriatic Sea The Adriatic Sea () is a body of water separating the Italian Peninsula from the Balkan Peninsula. The Adriatic is the northernmost arm of the Mediterranean Sea, extending from the Strait of Otranto (where it connects to the Ionian Sea) to t ...

at depths between . It lives on sand and muddy-sand bottoms into which it burrows to a depth of about .

Biology

''Amphiura filiformis'' lives submerged in soft substrate with part of its arms projecting above the surface of the sand for the purpose of suspension feeding and gas exchange. It feeds mostly on

zooplankton Zooplankton are the animal component of the planktonic community ("zoo" comes from the Greek word for ''animal''). Plankton are aquatic organisms that are unable to swim effectively against currents, and consequently drift or are carried along by ...

, but also consumes sediment and

detritus In biology, detritus () is dead particulate organic material, as distinguished from dissolved organic material. Detritus typically includes the bodies or fragments of bodies of dead organisms, and fecal material. Detritus typically hosts commun ...

when necessary. The arms are also used for removing sediment from the burrow. Juveniles reach maturity at three to four years of age and it is thought that the lifespan may be twenty years. Spawning takes place between July and September in the Irish Sea but lasts for a longer period in the Mediterranean. Females liberate large numbers of eggs into the sea where they are fertilised. The larvae are

ic and drift with the current. They can survive for about 88 days before settling on the seabed and undergoing metamorphosis into juveniles. It has been calculated that they can travel about in this time and this allows ''A. filiformis'' to expand its range, or recolonise areas where it has suffered mass deaths, as happened in a cold-related event in the

German Bight The German Bight (german: Deutsche Bucht; da, tyske bugt; nl, Duitse bocht; fry, Dútske bocht; ; sometimes also the German Bay) is the southeastern bight of the North Sea bounded by the Netherlands and Germany to the south, and Denmark and ...

in 1977. Mortality is very high among newly settled juveniles, perhaps because they are unable to bury themselves until they reach a certain size.

Ecology

In the southern North Sea, this species has become much more common during the second half of the 20th century. In the 1930s there was an average of about 69 individuals per square metre in suitable habitats, by 1950 this had dropped to 29 but by 1986, it had increased to 416 per square metre. A similar trend was observed in the

Skagerrak The Skagerrak (, , ) is a strait running between the Jutland peninsula of Denmark, the southeast coast of Norway and the west coast of Sweden, connecting the North Sea and the Kattegat sea area through the Danish Straits to the Baltic Sea. The ...

and

Kattegatt The Kattegat (; sv, Kattegatt ) is a sea area bounded by the Jutlandic peninsula in the west, the Danish Straits islands of Denmark and the Baltic Sea to the south and the provinces of Bohuslän, Västergötland, Halland and Skåne in Sweden i ...

area but not in the

Baltic Sea The Baltic Sea is an arm of the Atlantic Ocean that is enclosed by Denmark, Estonia, Finland, Germany, Latvia, Lithuania, Poland, Russia, Sweden and the North and Central European Plain. The sea stretches from 53°N to 66°N latitude and from ...

. It is suggested that this build up in numbers was mainly due to

eutrophication Eutrophication is the process by which an entire body of water, or parts of it, becomes progressively enriched with minerals and nutrients, particularly nitrogen and phosphorus. It has also been defined as "nutrient-induced increase in phytopla ...

of the North Sea, although overfishing of the

flatfish A flatfish is a member of the Ray-finned fish, ray-finned demersal fish order (biology), order Pleuronectiformes, also called the Heterosomata, sometimes classified as a suborder of Perciformes. In many species, both eyes lie on one side of the ...

that feed on the brittle stars may have played a minor role. An increase in nutrients led to an expansion of plankton and, as suspension feeders, the brittle stars benefited from an increased food supply. ''Amphiura filiformis'' is able to regenerate its arms if they are lost. A study in the North Sea found that only 4% of adults had a full complement of arms and the rest had damaged, missing or regenerating limbs. An examination of the stomach contents of their chief

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 ...

, the dab (''

Limanda limanda The common dab (''Limanda limanda'') is an edible flatfish of the family Pleuronectidae. It is a demersal fish native to shallow seas around Northern Europe, in particular the North Sea, where it lives on sandy bottoms down to depths of about . I ...

'') showed that the arms of these brittle stars formed an important part of their diet. The annual consumption of arms by the fish was calculated as about 420 arms per square metre of seabed, the equivalent of 6% of all the ''A. filiformis'' arms. Given the speed of regeneration of arms by the brittle stars, it was considered that this did not have a significant effect on the population size.

Use in research

''Amphiura filiformis'' has been used as a

model organism A model organism (often shortened to model) is a non-human species that is extensively studied to understand particular biological phenomena, with the expectation that discoveries made in the model organism will provide insight into the workin ...

for studying

stem cell In multicellular organisms, stem cells are undifferentiated or partially differentiated cells that can differentiate into various types of cells and proliferate indefinitely to produce more of the same stem cell. They are the earliest type o ...

s. The researchers were interested in studying how the nervous system recovered during arm regeneration as this could have applications for understanding and treating

neurodegenerative A neurodegenerative disease is caused by the progressive loss of structure or function of neurons, in the process known as neurodegeneration. Such neuronal damage may ultimately involve cell death. Neurodegenerative diseases include amyotrophic ...

diseases in humans.

References

{{Taxonbar, from=Q3278191 Amphiuridae Animals described in 1776 Taxa named by Otto Friedrich Müller