Solaster dawsoni Verrill, 1880

Common name(s): Dawson's sun star, Morning sun star

Synonyms:
Phylum Echinodermata
 Class Asteroidea
  Order Spinulosida
   Suborder Eugnathina
    Family Solasteridae
Solaster dawsoni collected from near Northwest Island, WA.  Scale is in centimeters
(Photo by: Dave Cowles, August 2005)
Description:  This large seastar has 8-16 rays (usually 11-12) and no pedicellariae.  Paxillae on the aboral surface are separated from each other by about their diameter and blunt (photo), so that the dorsal surface is rather smooth.  The ambulacral grooves have enlarged marginal plates along their margins.  Disk diameter is about 1/3 total diameter and the aboral surface does not have a prominent gray-blue streak radiating from the central disk and out each ray (but see photo below).  Rays taper gradually from base to tip.  Aboral surface usually brown or or grayish, but may be orange or mottled.  Diameter to 40 cm.

How to Distinguish from Similar Species:Pycnopodia helianthoides grows larger, has more rays, has pedicellariae, and has obvious ossicles projecting from the aboral surface.  Solaster stimpsoni has an orange or pink aboral surface with a grayish-blue streak radiating from the central disk out along each ray.

Geographical Range:  Point Franklin, Alaska to Monterey Bay, CA (uncommon in central California)

Depth Range:  Intertidal to 414 m (mostly subtidal)

Habitat:  Usually on rocky bottoms, but sometimes on gravel or sand

Biology/Natural History:  Solaster dawsoni is a predator on other seastars, including Solaster stimpsoni, other Solaster dawsoniLeptasterias hexactis, Evasterias troschelii, Dermasterias imbricata, Henricia leviuscula, Crossaster papposus,Pycnopodia helianthoides, and Mediaster aequalis.  It also has been seen to feed on the sea cucumbers Eupentacta quinquesemita, Psolus chitonoides, Cucumaria miniata, and young Parastichopus californicus, and on the nudibranch Tritonia festiva, which swims away rapidly when touched.  Many other seastars also move away quickly when touched by S. dawsoniS. dawsoni moves along with its leading rays raised, and lunges forward (at least fast for a seastar) when it touches another star.  S. stimpsoni, one of its favorite prey species, curls all its arms upward above the disk when encountered and sometimes wards off the attack.  In Auke Bay, Alaska, S. dawsoni seems to eat mainly green urchins Strongylocentrotus droebachiensis.  The commensal polychaete scaleworms Arctonoe vittata and Arctonoe fragilis are common on the star.  Spawning occurs in mid April in southern British Columbia.  Eggs are about 1 mm in diameter.  Juveniles often take refuge among the tubedwelling polychaete Phyllochaetopterus prolifica.



 
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References:

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

General References:
  Carefoot, 1977
  Harbo, 1999
  Johnson and Snook, 1955
  Kozloff, 1993
  McConnaughey and McConnaughey, 1985
  Morris et al., 1980
  Niesen, 1997
  O'Clair and O'Clair, 1998
  Ricketts et al., 1985
  Sept, 1999

Scientific Articles:

McEdward, Larry R. and Benjamin G. Miner, 2006.  Estimation and interpretation of egg provisioning in marine invertebrates.  Integrative and Comparative Biology 46:3 pp 224-232
 

Web sites:
 



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



Some S. dawsoni have a color pattern on the aboral surface, but note there are no blue-gray stripes running down the rays.



A view of the oral side of S. dawsoni

Mouth

Another view of the open mouth, this time underwater through aquarium glass.



The aboral ossicles or paxillae are well separated.  These are magnified.


The ossicles along the edge of the ambulacral groove (which is at the top in this photo) are enlarged into marginal plates.


This S. dawsoni is swallowing a Leptasterias hexactis that it captured.  Notice also the commensal Arctonoesp polychaete scaleworm on the ray.


This Solaster dawsoni (left) was found eating this Dermasterias imbricata on the right at low tide.
Photo by Brooke Reiswig, July 2006


A tiny Solaster dawsoni among hydroids.  Underwater photo by Kirt Onthank, August 2007

Small

This small individual is about 2.5 cm in total diameter.  Photo by Dave Cowles, July 2012

Paxillae-small

The paxillae of the small individual shown above look different from those of adults.  The sack-like prejections are papulae.  Photo by Dave Cowles, July 2012

Ray tips small

A closeup of the ray tips of the small individual above.  Photo by Dave Cowles, July 2012



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