''Evasterias troschelii'' 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 starfish in the

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

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. The oldest unambiguous fossils of the family date to the Late Cretaceous. Genera The World Regi ...

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

Kamchatka The Kamchatka Peninsula (, ) 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 western coastlines, respectively. Immediately offshore along the Pacific ...

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 an American scientist. He was interested particularly in marine biology. Stimpson became an important early contributor to the work of the Smithsonian Institution and later, director o ...

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 (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

was collected 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 ...

Washington Washington most commonly refers to: * George Washington (1732–1799), the first president of the United States * Washington (state), a state in the Pacific Northwest of the United States * Washington, D.C., the capital of the United States ** A ...

. 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, Education center, education and Research institute, research centers, created by the Federal government of the United States, U.S. government "for the increase a ...

. 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 Verril ...

in 1914, with as the

type species In International_Code_of_Zoological_Nomenclature, 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 spe ...

. 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 th ...

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 (: 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). ...

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

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; , ) are a group of four volcanic islands off the coast of mainland Alaska, in the Bering Sea, about north of Unalaska and 200 miles (320 km) southwest of Cape Newenham. The ...

, 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. San Francisco itself is further north along the coast, by about 75 miles (120 km), accessible via CA 1 and U ...

but it is rarely seen south of

. 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 ind ...

'').

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 sta ...

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 ...

e that develop from these form part of the

zooplankton Zooplankton are the heterotrophic component of the planktonic community (the " zoo-" prefix comes from ), having to consume other organisms to thrive. Plankton are aquatic organisms that are unable to swim effectively against currents. Consequent ...

and disperse with the currents.

Prey

The mottled star is 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 feeds largely on

bivalve molluscs 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 ...

. 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 Barnacles are arthropods of the subclass (taxonomy), subclass Cirripedia in the subphylum Crustacean, Crustacea. They are related to crabs and lobsters, with similar Nauplius (larva), nauplius larvae. Barnacles are exclusively marine invertebra ...

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 sea cradles or coat-of-mail shells or suck ...

s, gastropod molluscs,

tunicate Tunicates are marine invertebrates belonging to the subphylum Tunicata ( ). This grouping 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 ...

s and

brachiopod Brachiopods (), phylum (biology), phylum Brachiopoda, are a phylum of 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 e ...

s. Some species of

limpet Limpets are a group of aquatic snails with a conical gastropod shell, shell shape (patelliform) and a strong, muscular foot. This general category of conical shell is known as "patelliform" (dish-shaped). Existing within the class Gastropoda, ...

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 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 only extant family in the order (biology), order Mytilida, known ...

''. Researchers surmised that pollution of the marine environment with oil might result in the domination of the mussel in the low intertidal zone of the region.

Other species interactions

The scale worm '' Arctonoe fragilis'' 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 f ...

. The parasitic ciliate '' Orchitophrya stellarum'' 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 ...

. It makes its way to the

gonad A gonad, sex gland, or reproductive gland is a Heterocrine gland, 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 gon ...

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

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

'').

References

{{Taxonbar, from1=Q61468573), from2=Q939373 Asteriidae Echinoderms described in 1862