Scyra acutifrons Dana, 1851

Common name(s): Sharp-nosed crab

Synonyms:
Phylum Arthropoda
 Subphylum Crustacea
  Class Malacostraca
   Subclass Eumalacostraca
    Superorder Eucarida
     Order Decapoda
       Suborder Pleocyemata
        Infraorder Brachyura (true crabs)
         Section Brachyrhyncha
         Family Majidae
A male Scyra acutifrons from Swirl Rocks, WA.  Carapace width about 4.5 cm.
(Photo by: Dave Cowles, July 2000)
Description:  This majid crab has a flattened rostrum that is longer than wide but less than half the carapace length, and is widest near the middle (photo).  The carapace is triangular, has a projection or lump near the two posterolateral corners, but has no sharp projection or shelf on the anterolateral margin.  The chelipeds of males are usually longer than the walking legs, slender, and tipped with orange.  When at rest the crab often sits with its chelae near its mouth and its very long "elbows" projecting out in front.  The carapace is brown or tan but may be overgrown with sponges and bryozoans.  Carapace width to 4.5 cm.

How to Distinguish from Similar Species: Oregonia bifurca and Hyas lyratus have a lyre-shaped body and a toothed expansion of the carapace on both sides of the anterior half, plus the rostrum is widest at the base.  Pugettia gracilis, Pugettia producta, and Pugettia richii have a sharp projection to the side near the middle of the carapace.

Geographical Range: Kodiak, Alaska to Punta San Carlos, Mexico.  Uncommon south of Monterey Bay, CA

Depth Range: Mostly subtidal, to 220 m

Habitat: Rocky areas, especially around boulders densely covered with invertebrates.  Sometimes found on pilings.

Biology/Natural History: Feeds on detritus and sessile invertebrates.  Predators include rockfish (Sebastes atrovirens, S. chrysomelas and S. caurinus), kelp greenling Hexagrammos decagrammus,  and sculpins.  Seems to be often found around sea anemones.  May decorate slightly by putting a few pieces of algae on its rostrum.  Other algae and bryozoans seem to overgrow the carapace naturally.  This crab often sits with the anterior end pointed down.  Females may carry eggs nearly any time of year.  May reproduce several times a year.  This species has a terminal molt so full-grown adults will no longer grow (and the carapace can become overgrown with organisms)(photo)



 
 
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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:
  Hart, 1982
  Jensen, 1995
  Kozloff, 1993
  Morris et al., 1980

Scientific Articles:



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


This individual is hiding under a subtidal rock near Rosario.  Notice the characteristic pose with the elbows forward/out and the chelae held near the mouth. Underwater photo by Jim Nestler, July 2005
 

Dorsal measured
A view of another individual, captured between 100-120 m depth in the San Juan Channel.  Photo by Dave Cowles, August 2015.


 
 
The underside of males and females looks somewhat different:
Male underside Female underside
Male underside: Abdomen tapers toward a point at the end. The chelipeds have numerous blunt knobs on the ischium, merus, and carpus, in marginal rows and scattered. Photo by Dave Cowles, Aug 2017 Female underside: The abdomen is more squared off on the end, and the blunt knobs on the chelipeds are smaller as well as less numerous and prominent. Photo by Dave Cowles, August 2015


Barnacle encrusted
This individual is heavily encrusted with barnacles and bryozoans, suggesting that it has been quite some time since it has molted. It has likely reached terminal molt. Photo by Dave Cowles, August 2017
 



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