The purple sunstar, northern sunstar, or smooth sun star, ''Solaster endeca'', 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 ...

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

Solasteridae The Solasteridae are a family of sea stars. Genera The following genera are listed in the World Register of Marine Species: * '' Crossaster'' Müller and Troschel, 1840 * '' Heterozonias'' Fisher, 1910 * '' Laetmaster'' Fisher, 1908 * '' Lophas ...

Description

''Solaster endeca'' can grow to about across, but a more normal adult size is half that. It is a robust species with 9 or 10 arms (occasionally any number from seven to 13) set around a large disc. The aboral (upper) surface is formed of

calcareous Calcareous () is an adjective meaning "mostly or partly composed of calcium carbonate", in other words, containing lime or being chalky. The term is used in a wide variety of scientific disciplines. In zoology ''Calcareous'' is used as an adje ...

plates densely covered with paxillae, peg-like projections covered in tiny spinelets. No

pedicellaria 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 ...

e are present, but groups of two to three

gill A gill () is a respiratory organ that many aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow respiration on land provided they are ...

s are found between the plates. On the oral (under) surface, the row of plates on either side of the ambulacral groove bear two or three spines and several rows of shorter spines, with two rows of

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 ...

. ''S. endeca'' ranges in colour from greyish-cream to pinkish-purple. The arms are often turned up at the tips, showing the pale oral surface. It can be confused with '' Crossaster papposus '', the only British species with a similar number of arms, but ''S. endeca'' has a smoother aboral surface.

Distribution and habitat

The purple sun star occurs in the northeastern Atlantic Ocean and the North Sea at depths to . Its typical habitats are muddy sand, gravel, or rocky areas with deposited sediment. It is found in both sheltered and fairly exposed locations. It also has a

circumboreal The Circumboreal Region in phytogeography is a floristic region within the Holarctic Kingdom in Eurasia and North America, as delineated by such geobotanists as Josias Braun-Blanquet and Armen Takhtajan. It is the largest floristic region in t ...

distribution and is found round the coasts of

Greenland Greenland ( kl, Kalaallit Nunaat, ; da, Grønland, ) is an island country in North America that is part of the Kingdom of Denmark. It is located between the Arctic and Atlantic oceans, east of the Canadian Arctic Archipelago. Greenland is t ...

, northeastern Canada, and the East Coast of the United States as far south as the

Gulf of Maine The Gulf of Maine is a large gulf of the Atlantic Ocean on the east coast of North America. It is bounded by Cape Cod at the eastern tip of Massachusetts in the southwest and by Cape Sable Island at the southern tip of Nova Scotia in the northeast ...

. 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 a

vulnerable species A vulnerable species is a species which has been Conservation status, categorized by the International Union for Conservation of Nature as being threatened species, threatened with extinction unless the circumstances that are threatened species, ...

. It also occurs in the northeastern Pacific Ocean between northern

Alaska Alaska ( ; russian: Аляска, Alyaska; ale, Alax̂sxax̂; ; ems, Alas'kaaq; Yup'ik: ''Alaskaq''; tli, Anáaski) is a state located in the Western United States on the northwest extremity of North America. A semi-exclave of the U.S., ...

and

Puget Sound Puget Sound ( ) is a sound of the Pacific Northwest, an inlet of the Pacific Ocean, and part of the Salish Sea. It is located along the northwestern coast of the U.S. state of Washington. It is a complex estuarine system of interconnected ma ...

Biology

''S. endeca'' 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 ...

. In the Atlantic Ocean, it feeds on other starfish and

bivalve molluscs Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, bival ...

, but in the Pacific, its diet is mainly

sea cucumber Sea cucumbers are echinoderms from the class Holothuroidea (). They are marine animals with a leathery skin and an elongated body containing a single, branched gonad. Sea cucumbers are found on the sea floor worldwide. The number of holothuria ...

s and other

invertebrate Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate ...

s. In Britain, breeding takes place in the spring. Over a period of about a week, the female lays several thousand eggs in batches. These rise to the surface of the water where they are fertilised by sperm liberated by the male. The developing

larva A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. The ...

e become less buoyant after three days, feed on the yolks of their eggs, swim with cilia, and develop a pair of larval arms. After about 18 days, they sink to the sea bed, where each one attaches itself to the substrate with a sucker. Here it undergoes

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 ...

during which it develops a disc and first five and then more arms, a pair of tube feet, relatively long spines, red eyespots on the tips of the arms, a mouth, and an anus. After six weeks, the sucker is resorbed and the juvenile starfish begins to move about with its tube feet.

References

{{Taxonbar, from=Q2464524 Solaster Fauna of the Atlantic Ocean Fauna of the Pacific Ocean Animals described in 1771 Taxa named by Carl Linnaeus