Placetron wosnessenskii Schalfeew, 1892

Common name(s): Scaled crab
Synonyms:  Lepeopus forcipatus
Phylum Arthropoda
 Subphylum Crustacea
  Class Malacostraca
   Subclass Eumalacostraca
    Superorder Eucarida
     Order Decapoda
       Suborder Pleocyemata
        Infraorder Anomura
         Superfamily Paguroidea
          Family Lithodidae
Placetron wosnessenskii, subtidal from 20m depth, Sares Head.  Carapace width about 6 cm.
(Photo by: Dave Cowles July 1997)
Description: This lithodid crab has a wide, mostly soft abdomen (photo)(photo), which is not held as tightly against the underside of the thorax as some other species do.  The chelae are spoon-shaped and have setae along the edges; both are of similar size (picture).  The carapace and legs are covered with what looks like scales.  Colored greenish gray to reddish dorsally, lighter underneath (photo).  Walking legs may have some banding and yellow or orange near the tips.  Carapace width to 7.2 cm.

How to Distinguish from Similar Species: At first glance this crab looks superficially like the helmet crab Telmessus cheiragonus or even like the shield-back kelp crab Pugettia producta (both Brachyurans), but can be distinguished by the wide, soft abdomen, the scale-like appearance, and the modified 5th leg characteristic of Anomurans.

Geographical Range: Pribilof Islands to Puget Sound

Depth Range: Shallow subtidal to 110 m

Habitat: Vertical rock faces and overhangs associated with Metridium senile or Metridium giganteum, among boulders.

Biology/Natural History: Have been observed eating brittle stars.  Predators of this species include river otter.  The abdomen of the female is mostly covered with plates (photo); that of the male is soft with vestigial plates (photo).
We have sometimes observed this crab sheltering under the anemone Cribrinopsis fernaldi (photo).


 
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References:

Dichotomous Keys:
  Hart, 1982
  Kozloff 1987, 1996
 

General References:
Jensen, 1995
O'Clair and O'Clair, 1998

Scientific Articles:
 


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

Another photo of the species.  Dave Cowles, July 2001


Enlargements of the right and left chelae from the picture above.  Dave Cowles, July 2001


The broad abdomen of this species is soft, somewhat like leather; especially in the distal yellow portion visible above.  This appears to be a male abdomen.  See the photos below to compare with a female abdomen.  Photo by Dave Cowles, July 2001

This gravid female found subtidally on Sares Head is 7 cm across the carapace.  Photo by Dave Cowles, July 2012.  See more photos of her below.

Female abdomen

The underside of this female's abdomen is soft in part of it but has a rounded, hardened shield across the tip.  She is carrying eggs (see below).  Photo by Dave Cowles, July 2012

Female with eggs

This is the same female as shown above.  She is highly defensive of her abdomen but the crevice seen in this view shows that she is carrying many bright orange eggs.


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