Pisaster Brevispinus
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''Pisaster brevispinus'', commonly called the pink sea star, giant pink sea star, or short-spined sea star, is a
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), ...
of
sea star 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 northeast
Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five Borders of the oceans, oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean, or, depending on the definition, to Antarctica in the south, and is ...
. It was first described to science by William Stimson in 1857. The
type specimen In biology, a type is a particular wikt:en:specimen, specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally associated. In other words, a type is an example that serves to ancho ...
was collected on a sandy bottom, deep, near the mouth of
San Francisco Bay San Francisco Bay (Chochenyo language, Chochenyo: 'ommu) is a large tidal estuary in the United States, U.S. state of California, and gives its name to the San Francisco Bay Area. It is dominated by the cities of San Francisco, California, San ...
.


Description

The pink sea star has five thick arms and a large central disc. It is one of the largest sea stars in the world. While typically having a diameter of , monsters up to have been found. The largest animals may weigh . The upper, arboral, surface of this star is generally pink, sometimes with shadings of gray. The radius of the arms is 2.8 to 5.0 times the radius of the central disc. The central disc contains an obvious
madreporite The madreporite is a light colored calcareous opening used to filter water into the water vascular system of echinoderms. It acts like a pressure-equalizing valve. It is visible as a small red or yellow button-like structure, looking like a sma ...
on its upper surface. This structure filters water used by the animal. The mouth of the animal is found on the underside of the central disc. There are short, spines on the upper surface of the star. While a row of spines generally runs along the top of each arm, they are otherwise scattered across the animal in no particular pattern singly or in clumps of two or three. Both the upper surface and lower surfaces contain tiny pincers,
pedicellariae A pedicellaria (: 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 Echinoidea). ...
, which likely are used to get rid of encrusting organisms which would otherwise grow on the star. On the lower, or oral side of the star, deep grooves radiate from the mouth which contain four rows of
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 ...
. The star uses these to move around, and to capture its prey. The tube feet around the mouth are particularly long, at least equal to the radius of the central disc, to aid in digging prey from the sea bottom.


Distribution and habitat

This sea star occurs along the coast of North America from
Sitka, Alaska Sitka (; ) is a municipal home rule, unified Consolidated city-county, city-borough in the southeast portion of the U.S. state of Alaska. It was under Russian America, Russian rule from 1799 to 1867. The city is situated on the west side of Ba ...
to
La Jolla, California La Jolla ( , ) is a hilly, seaside neighborhood in San Diego, California, occupying of curving coastline along the Pacific Ocean. The population reported in the 2010 census was 46,781. The climate is mild, with an average daily temperature o ...
. It is found in
Puget Sound Puget Sound ( ; ) is a complex estuary, estuarine system of interconnected Marine habitat, marine waterways and basins located on the northwest coast of the U.S. state of Washington (state), Washington. As a part of the Salish Sea, the sound ...
. The pink sea star is found in relatively shallow water from the lower
intertidal zone The intertidal zone or foreshore is the area above water level at low tide and underwater at high tide; in other words, it is the part of the littoral zone within the tidal range. This area can include several types of habitats with various ...
to deep. The animal does not tolerate being out of water very well, so it is generally found on the beach only during very low tides. It prefers quiet waters such as bays and harbors rather than the open ocean coast. It lives on the sea bed, preferring sandy and muddy bottoms where its main prey is found. It can, however, sometimes be found on rocky bottoms or pilings. It avoids areas of low salinity.


Reproduction and life cycle

Pink sea stars are primarily gonochoric, which is to say that individuals are either male or female. Each arm contains two
gonads A gonad, sex gland, or reproductive gland is a mixed gland and sex organ that produces the gametes and sex hormones of an organism. Female reproductive cells are egg cells, and male reproductive cells are sperm. The male gonad, the testicle, ...
. These stars lift their central discs off the bottom to spawn, releasing their microscopic
gametes A gamete ( ) is a haploid cell that fuses with another haploid cell during fertilization in organisms that reproduce sexually. Gametes are an organism's reproductive cells, also referred to as sex cells. The name gamete was introduced by the Ge ...
into the water. Their eggs are in diameter. It is thought that groups of stars use environmental signals to coordinate spawning to increase the chances of fertilization. Once fertilization has occurred, the
zygote A zygote (; , ) is a eukaryote, eukaryotic cell (biology), 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 individ ...
develops into a
planktonic Plankton are the diverse collection of organisms that drift in water (or air) but are unable to actively propel themselves against currents (or wind). The individual organisms constituting plankton are called plankters. In the ocean, they pro ...
larva A larva (; : larvae ) is a distinct juvenile form many animals undergo before metamorphosis into their next life stage. Animals with indirect development such as insects, some arachnids, amphibians, or cnidarians typically have a larval phase ...
which feeds on small
algae Algae ( , ; : alga ) is an informal term for any organisms of a large and diverse group of photosynthesis, photosynthetic organisms that are not plants, and includes species from multiple distinct clades. Such organisms range from unicellular ...
. The larva proceeds through several developmental phases. It becomes a
gastrula Gastrulation is the stage in the early embryonic development of most animals, during which the blastula (a single-layered hollow sphere of Cell (biology), cells), or in mammals, the blastocyst, is reorganized into a two-layered or three-layered e ...
in 2 to 3 days, a
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 ...
in 5 days, and finally a
brachiolaria A brachiolaria is the second stage of larval development in many starfishes. It follows the bipinnaria. Brachiolaria have symmetry (biology)#Bilateral_symmetry, bilateral symmetry, unlike the adult starfish, which have a symmetry (biology)#Pentame ...
. Towards the end of the last stage the larva develops a large sack like structure, a
primordium A primordium (; : primordia; synonym: anlage), in embryology, is an Organ (anatomy), organ or tissue in its earliest recognizable stage of development. Cell (biology), Cells of the primordium are called primordial cells. A primordium is the simp ...
, and begins searching for a suitable surface on which to settle. After settling to the bottom, the larva develops into a juvenile sea star.


Feeding behavior

The pink sea star is a carnivore and scavenger. Its main prey is
bivalves Bivalvia () or bivalves, in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of aquatic molluscs (marine and freshwater) that have laterally compressed soft bodies enclosed by a calcified exoskeleton consis ...
. It hunts, captures, and eats cockles, including Nuttall's cockle'','' butter clams, jackknife clams, horse clams, littleneck clams, and geoduck clams. How it locates buried clams is unknown, but once it finds a buried clam it will dig down to it by using its tube feet to push bits of sediment from near its mouth to the ends of its arms. Holes as deep as have been observed. It is a slow-motion hunter; it may take it several days to dig its prey from the sediment, latch on to it with its tube feet, and pull the valves open. At this point, the star everts its stomach through its mouth and forces it into the shell. The star can push its stomach as far as from its mouth. The pink sea star secretes digestive fluids and eats the bivalve inside its own shell. This star is opportunistic in its feeding and will eat other animals besides bivalves when available. It will eat sand dollars, snails, including Kellet's whelk,
barnacles Barnacles are arthropods of the subclass Cirripedia in the subphylum Crustacea. They are related to crabs and lobsters, with similar nauplius larvae. Barnacles are exclusively marine invertebrates; many species live in shallow and tidal water ...
, polychaete worms, and small Dungeness crabs. It feeds on
carrion Carrion (), also known as a carcass, is the decaying flesh of dead animals. Overview Carrion is an important food source for large carnivores and omnivores in most ecosystems. Examples of carrion-eaters (or scavengers) include crows, vultures ...
, including dead fish and squid. It is competitive with sunflower stars and will fight with them over prey items.


Predators

Sea otters The sea otter (''Enhydra lutris'') is a marine mammal native to the coasts of the northern and eastern North Pacific Ocean. Adult sea otters typically weigh between , making them the heaviest members of the weasel fa ...
have been observed to rip off an arm of this sea star to eat the gonads inside.
Gulls Gulls, or colloquially seagulls, are seabirds of the subfamily Larinae. They are most closely related to terns and Skimmer (bird), skimmers, distantly related to auks, and even more distantly related to waders. Until the 21st century, most gul ...
will attempt to consume a pink sea star exposed at low tide. They are also preyed upon by other sea stars, such as the
morning sun star ''Solaster dawsoni'', the morning sun star, is a species of starfish in the family Solasteridae. It is found on either side of the northern Pacific Ocean. It has two subspecies: *''Solaster dawsoni arcticus'' Verrill, 1914 *''Solaster dawsoni daw ...
. Sheep crabs also eat these sea stars''.'' It is likely that the largest animals escape predation simply because of their size.


References

{{Taxonbar, from=Q3277686 Asteriidae Starfish described in 1857