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).
Return to Main Page
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
Here is another individual regenerating. Photo by Dave Cowles, 2019
This individual, photographed under the Keystone ferry
drawbridge, is purple in color. Photo by Dave Cowles, July
2011
This is a common color for the species. Photo by Dave Cowles, 2019
This is another color variant. Photo by Dave Cowles, August 2020
Authors and Editors of Page:
Dave Cowles (2005): Created original page
|