Oregonia gracilis Dana, 1851

Common name(s): Graceful decorator crab
Synonyms:
 Oregonia hirta
 Oregonia longimana
Phylum Arthropoda
 Subphylum Crustacea
  Class Malacostraca
   Subclass Eumalacostraca
    Superorder Eucarida
     Order Decapoda
      Suborder Pleocyemata
       Infraorder Brachyura (true crabs)
        Family Majidae
Oregonia gracilis, Two Harbors, CA.  Carapace 3 cm long.
(Photo by: Dave Cowles May 1997)
Description:  This majid crab has a heart-shaped (nearly triangular, wider at back)  carapace and long rostrum composed of two spinelike processes.  It also has a large curved postorbital spine just behind each eye (picture, picture).  Its legs are long and slender.  It often liberally decorates itself with algae, sponges, bryozoans, or hydroids which it attaches by hooking to fine, hooked setae.  Carapace length, including rostrum, up to 5 cm.  Carapace color is usually brown or tan, sometimes gray.  Fingers of chelipeds are white with pink or orange tips.

How to Distinguish from Similar Species: This is the only decorator crab with the long hooked spine behind the eye.  The carapace does not have a sharp anterolateral projection as seen in Pugettia producta.

Geographical Range: Bering sea to Monterey, CA; Japan

Depth Range: Intertidal to 436 m deep

Habitat: Most abundant on mixed composition bottoms

Biology/Natural History: This crab decorates more liberally than any of the other decorator crabs in this area.  During decoration, pieces of material are attached to specialized hooked setae and also interact with pappose setae.  The crab's chelae are small and delicate.  In males the chelipeds are longer than the walking legs, but in females they are shorter.  Will eat carrion.  Predators include Pacific halibut (Hippoglossus stenolepis).  In Puget Sound area, eggs may be carried during most seasons.  Recently hatched eggs are orange-red; eggs nearly ready to hatch are reddish-brown.


 
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References:

Dichotomous Keys:
  Coffin, 1952
  Flora and Fairbanks, 1966
  Hart, 1982
  Kozloff 1987, 1996
  Smith and Carlton, 1975
  Wicksten, 2009

General References:
  Jensen, 1995

Scientific Articles:
Berke, Sarah K. and Sarah A. Woodin, 2009.  Behavioral and morphological aspects of decorating in Oregonia gracilis (Brachyura Majoidea).  Invertebrate Biology 128:2 pp 172-181  

Burnett, Nicole, 2024: A practical identification guide to the zoeae of the invasive European green crab, Carcinus maenas (Linnaeus, 1758) (Decapoda: Brachyura: Carcinidae), and to the zoeae of the families of brachyuran crabs in Washington state, USA. Journal of Crustacean Biology 44:4.  doi.org/10.1093/jcbiol/ruae064


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


Note large spine behind the eye on this close-up.


Another view of Oregonia gracilis rostrum.    Note the postorbital spines.  Photo by Dave Cowles, July 2000


This Oregonia gracilis is festooned with hydroids and (tunicates?).  From 100 m depth, San Juan Channel.  Photo by Dave Cowles, July 2001


Here is the underside of another individual.  Note the long, thin legs and chelipeds, and the long hydroid attached to the rostrum.  Photo by Dave Cowles, July 2005


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