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

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 ...

starfish 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 ...

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 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 britt ...

. 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'' having just five.

Biology

The nine-armed sea star is a

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

molluscs Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant taxon, extant species of molluscs are recognized. The number of fossil sp ...

, small

crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group ...

s and

polychaete worms Polychaeta () is a paraphyletic class of generally marine annelid worms, commonly called bristle worms or polychaetes (). Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called chaetae, which are m ...

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

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 ...

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 locomo ...

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 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 ...

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 st ...

larva which drift with the

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 ...

. 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 or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation. Some inse ...

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, 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 fro ...

. 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 Luidia Fauna of the Atlantic Ocean Marine fauna of North America Marine fauna of South America Animals described in 1816 Taxa named by Jean-Baptiste Lamarck