''Evasterias troschelii'' 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 ...

of starfish in the

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

Asteriidae The Asteriidae are a diverse family of Asteroidea (sea stars) in the order Forcipulatida. It is one of three families in the order Forcipulatida. Genera The World Register of Marine Species lists these genera within the family Asteriidae (in a ...

. Its common names include the mottled star, false ochre sea star and Troschel's true star. It is found in

Kamchatka The Kamchatka Peninsula (russian: полуостров Камчатка, Poluostrov Kamchatka, ) is a peninsula in the Russian Far East, with an area of about . The Pacific Ocean and the Sea of Okhotsk make up the peninsula's eastern and wes ...

and the north western coast of North America.

Taxonomy

The description of this species was first formally published in 1862 by

William Stimpson William Stimpson (February 14, 1832 – May 26, 1872) was a noted American scientist. He was interested particularly in marine biology. Stimpson became an important early contributor to the work of the Smithsonian Institution and later, direc ...

under the name ''Asterias troschelii'' (Stimpson first presented the new species in a lecture at the Boston Society of Natural History in 1861). The

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...

was collected in

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 ...

Washington Washington commonly refers to: * Washington (state), United States * Washington, D.C., the capital of the United States ** A metonym for the federal government of the United States ** Washington metropolitan area, the metropolitan area centered on ...

. Only part of one arm still remains of this smallish specimen at the

United States National Museum The Smithsonian Institution ( ), or simply the Smithsonian, is a group of museums and education and research centers, the largest such complex in the world, created by the U.S. government "for the increase and diffusion of knowledge". Founded ...

. It was moved to the new genus '' Evasterias'' by

Addison Emery Verrill Addison Emery Verrill (February 9, 1839 – December 10, 1926) was an American invertebrate zoologist, museum curator and university professor. Life Verrill was born on February 9, 1839 in Greenwood, Maine, the son of George Washington Verrill a ...

in 1914, with as the

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specimen ...

. Verrill published five new

varieties Variety may refer to: Arts and entertainment Entertainment formats * Variety (radio) * Variety show, in theater and television Films * ''Variety'' (1925 film), a German silent film directed by Ewald Andre Dupont * ''Variety'' (1935 film), ...

(''alveolata'', ''densa'', ''parvispina'', ''rudis'' and ''subnodosa'') besides the

nominate Nomination is part of the process of selecting a candidate for either election to a public office, or the bestowing of an honor or award. A collection of nominees narrowed from the full list of candidates is a short list. Political office In the ...

variety, and also published ''E. acanthostoma'' in 1914. Alexander Michailovitsch Djakonov synonymised all of Verrill's varieties, but retained ''alveolata'' as a ''forma'', and also made Verrill's ''E. acanthostoma'' a form of ''E. troschelii'', leaving the species with three forms including the nominate.

Description

The mottled star is a large starfish with a radius of up to . It has a small disc and five long narrow arms often turned up at the tip. The widest point of the arms is a little distance away from the edge of the disc. The aboral (upper or dorsal) surface of the disc is covered with a network of calcareous plates with spines about long surrounded by smaller spines and crossed and straight

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 ...

, minute pincer-like structures with two jaws. There is an irregular line of white-tipped spines running down the centre of the arms and the whole upper surface is rough to the touch. On the oral (lower or ventral) surface a long

ambulacral groove Ambulacral is a term typically used in the context of anatomical parts of the phylum Echinodermata or class Asteroidea and Edrioasteroidea. Echinoderms can have ambulacral parts that include ossicles, plates, spines, and suckers. For example, sea ...

stretches from the central mouth to the tip of each arm with four 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 ...

and clumps of pedicellariae and spines on either side. The colour is very variable and includes plain or mottled shades of orange, brown, greenish-grey, bluish-grey and pale purple. The outer edges of the arms often have a contrasting coloured rim and the underside is pale brown.

Distribution and habitat

''Evasterias troschelii'' is found on the west coast of North America. Its range extends from

Pribilof Islands The Pribilof Islands (formerly the Northern Fur Seal Islands; ale, Amiq, russian: Острова Прибылова, Ostrova Pribylova) are a group of four volcanic islands off the coast of mainland Alaska, in the Bering Sea, about north of ...

, Alaska southwards to

Monterey Bay, California Monterey Bay is a bay of the Pacific Ocean located on the coast of the U.S. state of California, south of the San Francisco Bay Area and its major city at the south of the bay, San Jose. San Francisco itself is further north along the coast, by a ...

but it is rarely seen south of

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 ...

. It also occurs in

( Bechevinskaya Bay). It is usually found on rocks and pebbles and occasionally on sand, at depths down to about or . In bays and other sheltered locations it largely replaces the other common species of the area, the purple sea star (''

Pisaster ochraceus ''Pisaster ochraceus'', generally known as the purple sea star, ochre sea star, or ochre starfish, is a common seastar found among the waters of the Pacific Ocean. Identified as a keystone species, ''P. ochraceus'' is considered an important indi ...

'').

Ecology

Breeding

In the north of its range, breeding takes place from April to June. Large numbers of small eggs are produced and fertilisation is external. The

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 s ...

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 that develop from these form part of the

zooplankton Zooplankton are the animal component of the planktonic community ("zoo" comes from the Greek word for ''animal''). Plankton are aquatic organisms that are unable to swim effectively against currents, and consequently drift or are carried along by ...

and disperse with the currents.

Prey

The mottled star 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 feeds largely on

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 ...

. With its tube feet it can exert a powerful traction on the two valves of a mollusc shell, pulling them sufficiently far apart to insert part of its stomach through the gap. It then uses digestive enzymes to break down the mollusc's tissues before sucking them out and removing its stomach from the shell. It also consumes

barnacle A barnacle is a type of arthropod constituting the subclass Cirripedia in the subphylum Crustacea, and is hence related to crabs and lobsters. Barnacles are exclusively marine, and tend to live in shallow and tidal waters, typically in eros ...

chiton Chitons () are marine molluscs of varying size in the class Polyplacophora (), formerly known as Amphineura. About 940 extant and 430 fossil species are recognized. They are also sometimes known as gumboots or sea cradles or coat-of-mail s ...

s, gastropod molluscs,

tunicate A tunicate is a marine invertebrate animal, a member of the subphylum Tunicata (). It is part of the Chordata, a phylum which includes all animals with dorsal nerve cords and notochords (including vertebrates). The subphylum was at one time ca ...

s and

brachiopod Brachiopods (), phylum Brachiopoda, are a phylum of trochozoan animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear end, w ...

s. Some species of

limpet Limpets are a group of aquatic snails that exhibit a conical shell shape (patelliform) and a strong, muscular foot. Limpets are members of the class Gastropoda, but are polyphyletic, meaning the various groups called "limpets" descended indep ...

exhibit behavioural responses to the presence of the mottled star and are able to evade it. Petroleum hydrocarbons, such as those released as a result of the

Exxon Valdez ''Oriental Nicety'', formerly ''Exxon Valdez'', ''Exxon Mediterranean'', ''SeaRiver Mediterranean'', ''S/R Mediterranean'', ''Mediterranean'', and ''Dong Fang Ocean'', was an oil tanker that gained notoriety after running aground in Prince Wil ...

spillage, have a greater effect on the feeding and growth of the mottled star than on one of its main prey species, the mussel ''

Mytilus edulis The blue mussel (''Mytilus edulis''), also known as the common mussel, is a medium-sized edible marine (ocean), marine bivalve mollusc in the family (biology), family Mytilidae, the mussels. Blue mussels are subject to commercial use and intensiv ...

''. Researchers surmised that pollution of the marine environment with oil might result in the

domination Domination or dominant may refer to: Society * World domination, which is mainly a conspiracy theory * Colonialism in which one group (usually a nation) invades another region for material gain or to eliminate competition * Chauvinism in which ...

of the mussel in the low intertidal zone of the region.

Other species interactions

The scale worm ''

Arctonoe fragilis ''Arctonoe'' is a genus of worms belonging to the family Polynoidae. They are commonly known as "scale worms". Members of this genus predominantly occur in shallow (50 metres or less) waters of the northeast Pacific Ocean and often live as commen ...

'' is often found living on the surface or in an ambulacral groove of the mottled 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 ...

. The parasitic ciliate ''

Orchitophrya stellarum ''Orchitophrya stellarum'' is a species of single-celled marine ciliates, a member of the class Oligohymenophorea. It is found living freely in the north Atlantic and Pacific Oceans but is also parasitic, being found inside the gonads of starfish ...

'' has several hosts, one of which is the mottled star. It lives among the spines on the body and arms until the starfish is ready to breed when it moves inside its host, probably entering through a

gonopore A gonopore, sometimes called a gonadopore, is a genital pore in many invertebrates. Hexapods, including insects have a single common gonopore, except mayflies, which have a pair of gonopores. More specifically, in the unmodified female it is the ...

. It makes its way to the

gonad A gonad, sex gland, or reproductive gland is a mixed gland 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, produces sper ...

s of the male starfish and feeds on the sperm, effectively castrating its host. Juvenile Alaskan king crabs ''(

Paralithodes camtschaticus The red king crab (''Paralithodes camtschaticus''), also called Kamchatka crab or Alaskan king crab, is a species of king crab native to the Bering Sea and Gulf of Alaska. It was introduced to the Barents Sea. It grows to a leg span of , and is ...

)'' have been observed living as commensals on the surface of the mottled star, sheltering between its arms. Adult king crabs have been reported as attacking and eating the starfish. It is also preyed on by gulls in the intertidal zone and by the morning sunstar (''

Solaster dawsoni ''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: *''S. d. arcticus'' Verrill, 1914 *''S. d. dawsoni'' Verrill, 1880 ...

'') and the sunflower seastar (''

Pycnopodia helianthoides ''Pycnopodia helianthoides'', commonly known as the sunflower sea star, is a large sea star found in the northeast Pacific. The only species of its genus, it is among the largest sea stars in the world, with a maximum arm span of . Adult sunflow ...

'').

References

{{Taxonbar, from=Q939373 Asteriidae Animals described in 1862