Stomphia didemon Siebert, 1973  Common name(s): Orange anemone.  Swimming anemone.  Apple anemone.
Synonyms: Actinostola sp.
Phylum Cnidaria  Class Anthozoa    Subclass Zoantharia     Order Actiniaria      Family Actinostolidae
	Stomphia didemon, about 3.5 cm diameter and 4 cm tall.  Captured by otter trawl at about 90 m depth from San Juan Channel
	Photo by: Dave Cowles July 2001

How to Distinguish from Similar Species: Stomphia coccinea has a whitish column with red or orange-red streaks, is not usually more than 3 cm high, and usually is found on horse mussel (Modiolus modiolus) shells.  Stomphia sp. has less than 130 tentacles on individuals 5 cm or more tall, and its color is a uniform reddish beige.

Geographical Range:  Web sources indicate that it can be found at least in Alaska, British Columbia, and Washington State.

Depth Range:  The Monterey Bay Aquarium reports that this species lives from 60-180 m depth (http://www.mbayaq.org/efc/living_species/default.asp?hOri=0&hab=9&inhab=495)

Habitat: In the San Juan channel specimens are often captured from sand/gravel bottoms at about 80-100 m depths.  They usually come up not attached to anything, though they will readily attach to a solid object in an aquarium.  Perhaps this is because they have a swimming response to predators.

Biology/Natural History:  Little is known.  This is a recently described species.  The spincter of Stomphia species in general is strong enough that the upper part of the body can cover the tentacles (the tentacles can be retracted completely inside).  This species, as well as Stomphia coccinea, are known to detach from the bottom and swim away from predators such as the leather star, Dermasterias imbricata.  S. coccinea is found in northern boreal waters of the Atlantic and Pacific.  Another relative, S. selaginella, inhabits McMurdo Sound in Antarctica. Click the photo below to see a movie of the anemone doing this in our laboratory. However, the anemone did not seem to have any reaction in the laboratory to the rose star Crossaster papposus, another star that lives at similar depths and is often caught in the same trawls.
On one web site (http://www.bbc.co.uk/nature/animals/features/292feature1.shtml), the BBC reports on S. didemon: "When approached by a predatory leather star, this anemone, Stomphia didemon, became highly agitated. It elongated and swayed from side to side. Then, bending low, it brushed its tentacles over the leather star. Finally, this normally sedentary animal inflated a muscular cone at its base to lever itself free from its moorings and danced away in the water column."
This species is said to eat small crustaceans.

References:

Dichotomous Keys:

General References:
  Lamb and Hanby, 2005
 

Web References:
http://www.underwater-photos.com/pw046.html (a photo and short note on S. coccinea)
http://www.ups.edu/faculty/jkelliott/escape.htm (photos and description of S. didemon escaping from the leather star)
 

Scientific Articles:

Dalby, J. Jr., J. K. Elliott, and D. M. Ross. 1988. The swimming response of the actinian Stomphia didemon to certain asteroids: distributional and phylogenetic implications. Can. J. Zool. 66: 2484-2491.

Stomphia didemon's column wall.  This species has no tubercles or acontia on the wall.  A few bits of debris may be present but they appear to be just loosely attached by mucus.


Another individual.  Captured 100 m depth, San Juan Channel.  Photo by Dave Cowles, July 2000

A view of the oral disk.  Photo by Dave Cowles, July 2000

This individual from 100 m, San Juan Channel, is perched on a shell.

The tentacles end with a small pore.

An unusually pale individual.
 

This species does indeed swim when the seastar Dermasterias imbricata encounters it. Click on the photo above to see it in live action. Just before the video started, the Dermasterias seastar was placed near the anemone and began slowly crawling toward it. As the seastar came very close, the anemone first extended its tentacles down and touched the surface of the seastar. About 10 seconds later, just before this video began, the anemone suddenly leaned sharply toward the seastar. Then, as seen in the video, it quickly partially retracted its tentacles, disconnected its foot, and swam away like a contorting umbrella. Photo and video by Abigail Cooley at Rosario Beach Marine Lab, July 2025.