''Luidia ciliaris'', the seven-armed sea 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 ...

sea star Starfish or sea stars are star-shaped echinoderms belonging to the class Asteroidea (). Common usage frequently finds these names being also applied to ophiuroids, which are correctly referred to as brittle stars or basket stars. Starfish a ...

(starfish) in the family Luidiidae. It is found in the eastern

Atlantic Ocean The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe ...

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 ...

Description

''L. ciliaris'' is an orangeish-brown colour and has seven long arms radiating from a small disk. It is a large but fragile sea star, growing to across, and easily losing its arms (which afterwards regenerate). The arms have parallel sides and taper only near the tip. They have a conspicuous fringe of white spines along the margins. The upper surface is clothed in paxillae, spines shaped like a pillar with a flat top bearing tiny spinules. Also, many-lobed, nipple-like papillae are seen. No marginal plates are on the upper side of the arms, but those on the lower side bear

pedicellariae A pedicellaria (plural: pedicellariae) is a small wrench- or claw-shaped appendage with movable jaws, called valves, commonly found on echinoderms (phylum Echinodermata), particularly in sea stars (class Asteroidea) and sea urchins (class Echinoi ...

with two valves. 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 ...

are long and numerous. They do not have suction pads, but have two sets of terminal bulbs. The gonads are arranged in two rows along the length of the arms. A mouth is at the centre of the underside, with an oesophagus and a cardiac stomach, but no intestine, pyloric stomach, or anus.Seven-armed starfish - ''Luidia ciliaris''

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 2011-08-29.

Distribution and habitat

''L. ciliaris'' occurs on the

seabed The seabed (also known as the seafloor, sea floor, ocean floor, and ocean bottom) is the bottom of the ocean. All floors of the ocean are known as 'seabeds'. The structure of the seabed of the global ocean is governed by plate tectonics. Most of ...

in the eastern

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 the ...

and the

Faroe Islands The Faroe Islands ( ), or simply the Faroes ( fo, Føroyar ; da, Færøerne ), are a North Atlantic island group and an autonomous territory of the Kingdom of Denmark. They are located north-northwest of Scotland, and about halfway bet ...

southwards to Cape Verde and 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 in the

. It is found in the

neritic zone The neritic zone (or sublittoral zone) is the relatively shallow part of the ocean above the drop-off of the continental shelf, approximately in depth. From the point of view of marine biology it forms a relatively stable and well-illuminated ...

at depths down to , mainly on soft sediments into which it sometimes burrows, but sometimes on rock.

Biology

''L. ciliaris'' 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 ...

and scavenger and feeds predominantly on 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 s ...

s. A study in the Irish Sea found that the

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 ...

s, ''

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 ...

'' and ''

Ophiura albida ''Ophiura albida'' is a species of brittle star in the order Ophiurida. It is typically found on the seabed in the north eastern Atlantic Ocean and in the Mediterranean Sea and is sometimes known as the serpent's table brittle star. Description ...

'', and the sea urchin, '' Psammechinus miliaris'', formed the chief items of prey. The brittle star '' Ophiocomina nigra'' was also consumed, but in lesser quantities because it had more efficient escape strategies. The seven-armed sea star moves rapidly in comparison with other sea stars. It hoists itself up on the tips of its arms, in which position it can "walk", before launching itself at its

prey 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 ...

. The ring of plates around its mouth are extensible or can even be ruptured to enable it to ingest food items much bigger than the normal size of its mouth. In this way, it can pounce on a brittle star in diameter and completely engulf it. Undigested remains are ejected through the mouth.''Luidia ciliaris''
Animal Diversity Web. Retrieved 2011-08-30. ''L. ciliaris'' breeds in early summer. Each female releases millions of

eggs Humans and human ancestors have scavenged and eaten animal eggs for millions of years. Humans in Southeast Asia had domesticated chickens and harvested their eggs for food by 1,500 BCE. The most widely consumed eggs are those of fowl, especial ...

into 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 ...

, which stimulates the release of sperm by the males. About 4 days after fertilisation, the

zygote A zygote (, ) is a eukaryotic cell formed by a fertilization event between two gametes. The zygote's genome is a combination of the DNA in each gamete, and contains all of the genetic information of a new individual organism. In multicell ...

s develop into

bipinnaria A bipinnaria is the first stage in the larval development of most starfish, and is usually followed by a brachiolaria stage. Movement and feeding is accomplished by the bands of cilia. Starfish that brood their young generally lack a bipinnaria st ...

l larvae, which form part of the

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 ...

. After several moults, the seven arms can be seen developing in what is called the "rudiment", which is connected to a stalk with several bands of cilia. The larvae reach a length of in 3 to 4 months. It does not become a brachiolarial larva as is the case in most sea star

taxa In biology, a taxon (back-formation from ''taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular nam ...

. Instead, it settles on the sea bed and metamorphosis takes place. Functional tube feet appear in the juvenile before the larval tissue is fully reabsorbed.Zooplankton and Micronekton of the North Sea: ''Luidia ciliaris''
Marine Species Identification Portal. Retrieved 2011-08-28.

References

{{Taxonbar, from=Q2014285 Luidia Fauna of the Atlantic Ocean Fauna of the Mediterranean Sea Animals described in 1837 Taxa named by Rodolfo Amando Philippi