Orthasterias koehleri (de Loriol, 1897)
Common name(s): Rainbow star, long-armed sea star, longrayed starfish, red banded sea star, painted star, fragile star
|Synonyms: Asterias koehleri, Orthasterias columbiana|
|Orthasterias koehleri from 70 m depth, San Juan Channel. This individual recently lost two of its rays. Ray length is 20 cm.|
|(Photo by: Dave Cowles, July 2008)|
How to Distinguish from Similar Species: Stylasterias forreri is similar in shape and spines but is brown, olive, or gray without red and has differences in its spines and pedicellariae. Evasterias troschelii has a generally similar body shape and variable coloration but its rays are thickest a short distance from the central disk and it does not have the pronounced series of large spines surrounded by fleshy cushions of pedicellariae.
Geographical Range: Eastern Aleutian Islands to northern Mexico.
Depth Range: Intertidal or (usually) subtidal to 283 m or more
Habitat: Rock, pebbles, sand, and mud
Biology/Natural History: Studies
have indicated that this species may eat a variety of prey such as snails,
limpets, bivalves, chitons, squid, brachiopods, barnacles, crabs, fish,
and tunicates but it seems to especially eat bivalves. It can use
its large tube feet to pull clams up out of the sediment, then chips away
some of the margin of the shell until it can insert its stomach and digest
the clam. Breeding occurs from June to August. Spawning individuals
elevate themselves from the bottom on their arm tips. Lifespan is
at least 9 years. The polychaete worm Arctonoe
fragilis is commensal on this seastar (photo).
|Main Page||Alphabetic Index||Systematic Index||Glossary|
Furlong and Pill, 1972
Gotshall and Laurent, 1979
Johnson and Snook, 1955 (As Orthasterias columbiana)
Lamb and Hanby, 2005
Morris et al., 1980
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:
Older references such as Johnson and Snook (1955) state that this species is common intertidally. However, my experience and several more recent references confirm that now this species is much less common intertidally than subtidally.
This aboral view (in other words, view from the top) of the ray shows the line of large carinal spines down the aboral surface and the ragged rows of spines on each side. Notice the cushions of small pedicellariae which surround each spine. Also notice the large individual pincer-like pedicellariae and the abundant papulae between the spines. Photo by Dave Cowles, July 2008
This lateral view of the rays shows the scattered rows of spines, the abundant large pedicellariae and papulae among the spines, and the rows of adambulacral spines along the bottom.
|Views of the oral (ambulacral) region of the rays. Photos by Dave Cowles, July 2008|
|This lateral view of the ambulacral area of the rays shows the scattered rows of ray spines surrounded by cushions of small pedicellariae along the sides of the ray. Below that is a section of prominent papulae which are largely obscuring the row of small oral intermediate spines. At the bottom of the ray can be seen the forked adambulacral spines which also have pedicellariae around them, and the tube feet are at the very bottom.||This oral (ambulacral) view of a ray shows the 4 rows of long tube feet. The forked adambulacral spines are visible along the margins of the ambulacral groove, though the tissue around the spines is so dense that the two forks look like two separate rows. The mouth plates, which are between the ambulacral groove and the adambulacral spines are apparently sunken and not visible.|
This closeup view shows the abundant pedicellariae and papulae among the large spines. The small crossed pedicellariae in the cushions around the spines are mostly retracted in this view but a number of the individual pedicellariae between the spines are open.
The polychaete worm Arctonoe fragilis is often found as a commensal on this seastar. I cannot distinguish the dorsal plates (elytra) on this worm but perhaps they have broken off and simply left the white bases. The worm seems to spend the large majority of the time on the aboral surface of the rays, even though that is where all the large pedicellariae are. I wonder what kind of relationship it and the seastar have that prevents the worm from being severely pinched?