Evasterias troschelii (Stimpson, 1862)
Common name(s): Mottled star. False ochre sea star; Troschell's true star
|Evasterias troschelii subtidal from Sares Head, WA. Ruler is 6 inches|
|(Photo by: Dave Cowles, July 2001)|
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.
Gotshall and Laurent, 1979
Morris et al., 1980
O'Clair and O'Clair, 1998
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
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
This individual, photographed under the Keystone ferry drawbridge, is purple in color. Photo by Dave Cowles, July 2011