Evasterias troschelii (Stimpson, 1862)

Common name(s): Mottled star. False ochre sea star; Troschell's true star
Synonyms:
Phylum Echinodermata
 Class Asteroidea
  Order Forcipulatida
   Suborder Asteriadina
   Family Asteriidae
Evasterias troschelii subtidal from Sares Head, WA.  Ruler is 6 inches
(Photo by: Dave Cowles, July 2001)
Description:  This seastar has a small central disk and 5 long rays (total diameter is 5 to 7.6 times central disk diameter) which are not bordered by obvious marginal plates (photo).  The rays usually narrow as they attach to the central disk and are widest at a point slightly out from the central disk.   Exposed ossicle spines (less than 2 mm high, irregular pattern) and pedicellariae make the aboral surface rough (photo).  Clusters of pedicellariae are especially visible near the ambulacral grooves, and are usually in clumps at the bases of spines. Has both crossed and straight pedicellariae.  Color highly variable:  gray, blue-gray, greenish, brown, orange, reddish (especially along the Oregon and California coast), pale purple; frequently margins of rays are a different shade than aboral surface.  Radius up to 28 cm.

How to Distinguish from Similar Species: Small individuals look somewhat like a Pisaster ochraceous or P. brevispinus, but this species has longer rays in proportion to its central disk and the rays narrow before they meet the central disk, and the aboral ossicles are not arranged in a clustering network.

Geographical Range: Pribilof Islands, Alaska to Monterey Bay, CA; Kamchatka.  Uncommon south of Puget Sound.  This is the most abundant large, intertidal star in the Juneau area.

Depth Range: Low intertidal and subtidal to 70 m.  Mostly subtidal in the Rosario area (abundant in eelgrass).

Habitat: On rocks and cobbles (occasionally sand); sometimes on docks and pilings.  More abundant intertidally in protected areas than along the open coast.

Biology/Natural History: Feeds on a variety of animals--bivalves, limpets, snails, brachiopods, barnacles, and tunicates.  Can evert its stomach (up to a distance equal to half the length of a ray).  Several limpets exhibit escape responses from this species.  May have a symbiotic scaleworm (Arctonoe fragilis) living in the ambulacral groove or on the body surface (photo).  In Alaska one can often find the young of the Alaska King Crab (Paralithodes camtschaticus) nestled between the rays of this seastar.  Predators include gulls (especially in Alaska where they are common intertidally), Solaster dawsoni,and Pycnopodia helianthoides; and attacks by the rose star Crossaster papposus and by Alaska King Crab Paralithodes camtschaticus have been observed.  Tolerant of reduced salinities down to 20 ppt.

In Burrard Inlet, BC, Canada, this species became more abundant in the intertidal after seastar wasting disease while Pisaster ochraceus became less abundant. This species can be infected but seems less susceptible to infection by seastar wasting disease than is P. ochraceus (Kay et al., 2019).


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References:

Dichotomous Keys:
Flora and Fairbanks, 1966
Kozloff 1987, 1996
Smith and Carlton, 1975

General References:
Gotshall and Laurent, 1979
Kozloff, 1993
Morris et al., 1980
O'Clair and O'Clair, 1998

Scientific Articles:
Kay, S.W.C., A.M. Gehman, and C.D.G. Harley, 2019. Reciprocal abundance shifts of the intertidal sea stars, Evasterias troschelii and Pisaster ochraceus, following sea star wasting disease. Proceedings of the Royal Society of London Part B: Biological Sciences 286:1901 p  doi: 10.1098/rspb.2018.2766

Knott, K. Emily, and Gregory A. Wray, 2000. Controversy and consensus in Asteroid systematics: new insights to Ordinal and Familial relationships. American Zoologist 40:3 pp. 382-392

Mauzey, K.P., C. Birkeland, and P.K. Dayton, 1968.  Feeding behavior of asteroids and escape responses of their prey in the Puget Sound region.  Ecology 49: 603-619
 


General Notes and Observations:  Locations, abundances, unusual behaviors:

This species is commonly found off Sares Head.



Another individual, with three symbiotic Arctonoe sp scaleworms attached.  Ruler is 1 foot (30 cm).  Photo by Dave Cowles, July 2005
 



The aboral surface has large spines (1-2 mm long) arranged singly.  Smaller spines and pedicellariae are arranged in circles around the large spines.
Photo by Dave Cowles, July 2005
 



There are no large marginal plates on the rays.  The stomach can be everted, as it was shortly before this photo.  Photo by Dave Cowles, July 2005


This view of the aboral side of the central disk shows the networklike system of spiny ossicles.  Photo by Dave Cowles, July 2008
 


The scaleworm Arctonoe fragilis is a common symbiont on this and other seastar species.  Photo by Dave Cowles July 2005


This individual, with individual rays from 25-30 cm long, was collected by otter trawl from 75 m depth in San Juan Channel.
Notice that it has lost one ray which it is beginning to regenerate.  Photo by Dave Cowles, July 2008

Evasterias troschelii regenerating
Here is another individual regenerating. Photo by Dave Cowles, 2019

Purple

This individual, photographed under the Keystone ferry drawbridge, is purple in color.  Photo by Dave Cowles, July 2011

Purple color
This is a common color for the species. Photo by Dave Cowles, 2019

Another color variant

This is another color variant. Photo by Dave Cowles, August 2020


Authors and Editors of Page:
Dave Cowles (2005):  Created original page