''Luidia senegalensis'', the nine-armed sea star, is a tropical

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

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

in the family Luidiidae found in the western Atlantic Ocean.

Description

The nine-armed sea star has long, slim tapering arms attached to a small circular central disc. It grows to a diameter of about . The aboral or upper surface has a patchwork of closely packed spiny plates. The square ones near the edge of the arms are cream coloured and the irregular ones in a band running down the middle of the arms are grey. The margins of the arms are fringed with short white spines. The oral or underside of the sea star has further small white spiny plates down the edges of the arms and a central band of translucent, orange

tube feet Tube or tubes may refer to: * Tube (2003 film), ''Tube'' (2003 film), a 2003 Korean film * "Tubes" (Peter Dale), performer on the Soccer AM#Tubes, Soccer AM television show * Tube (band), a Japanese rock band * Tube & Berger, the alias of dance/e ...

. Like other members of its genus, it has tube feet without suckers. The mouth is at the centre of the disc and there is no anus, undigested food fragments being expelled through the mouth.

Distribution and habitat

The nine-armed sea star is found at depths of up to around the coasts of Florida, in the Caribbean Sea, the Gulf of Mexico, and along the coast of South America to southern Brazil. It favours sandy, muddy or shelly

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 ...

s in sheltered locations such as lagoons. It occupies the same range as the closely related gray sea star (''Luidia clathrata'') and has a very similar colouring but is easily distinguished by the number of arms, ''L. clathrata'' Nine.

Biology

The nine-armed sea star is a

scavenger Scavengers are animals that consume Corpse decomposition, 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 he ...

and a

predator Predation is a biological interaction in which one organism, the predator, kills and eats another organism, its prey. It is one of a family of common List of feeding behaviours, feeding behaviours that includes parasitism and micropredation ...

and examination of the stomach contents show that the diet consists primarily of

molluscs Mollusca is a phylum of protostome, protostomic invertebrate animals, whose members are known as molluscs or mollusks (). Around 76,000 extant taxon, extant species of molluscs are recognized, making it the second-largest animal phylum ...

, small

crustacean Crustaceans (from Latin meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of arthropods that are traditionally a part of the subphylum Crustacea (), a large, diverse group of mainly aquatic arthrop ...

s and polychaete worms. Many of the food items were swallowed whole and had been ingested by the starfish everting its stomach and engulfing its prey. It also buries itself in the

substrate Substrate may refer to: Physical layers *Substrate (biology), the natural environment in which an organism lives, or the surface or medium on which an organism grows or is attached ** Substrate (aquatic environment), the earthy material that exi ...

and engulfs "mouthfuls" of sediment, filtering it through its oral spines and extracting

detritus In biology, detritus ( or ) is organic matter made up of the decomposition, decomposing remains of organisms and plants, and also of feces. Detritus usually hosts communities of microorganisms that colonize and decomposition, decompose (Reminera ...

and small organisms such as

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. Breeding takes place at different times of the year in different parts of the range. The sea stars liberate their gametes into the sea where fertilisation takes place. The eggs hatch 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 sta ...

larva which drift with the

plankton Plankton are the diverse collection of organisms that drift in Hydrosphere, water (or atmosphere, air) but are unable to actively propel themselves against ocean current, currents (or wind). The individual organisms constituting plankton are ca ...

. In about 25 days they have grown considerably and settle on the sea bed before undergoing

metamorphosis Metamorphosis is a biological process by which an animal physically develops including birth transformation or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and different ...

into juvenile sea stars. In polluted waters, the nine-armed sea star has been found to concentrate heavy metals into its tissues. Zinc, and to a lesser extent nickel, lead, cadmium and silver accumulate in the body wall and the pyloric caeca (parts of the gut which project into the arms). In the

Indian River Lagoon The Indian River Lagoon is a grouping of three lagoons: the Mosquito Lagoon, the Banana River, and the Indian River, on the Atlantic Coast of Florida; one of the most biodiverse estuaries in the Northern Hemisphere and is home to more than 4, ...

, a small brown polychaete worm sometimes lives on the surface of the sea star 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 f ...

. There may be several on one sea star and they probably benefit from the stirring up of the sediment caused by the sea star's activities.

References

External links

* {{Taxonbar, from=Q3199442 senegalensis Echinoderms of the Atlantic Ocean Marine fauna of North America Marine fauna of South America Starfish described in 1816 Taxa named by Jean-Baptiste Lamarck