Pinnixa eburna Wells, 1928

Common name(s):  Arenicolid pea crab, Lugworm pea crab
Synonyms: Pinnixa eburnea Pinnixa eburna
Phylum Arthropoda 
Subphylum Crustacea 
Class Malacostraca 
Subclass Eumalacostraca 
Superorder Eucarida 
Order Decapoda 
Suborder Pleocyemata 
Pinnixa eburna, carapace width 7 mm wide by 3.5 mm long.  Found in a burrow of Abarenicola pacifica on the mudflats of Padilla Bay.
(Photo by: Dave Cowles, June 2009)
Description:   This pea crab has a hard, smooth, oval carapace width about twice the length, with rounded, setose lateral margins.  The walking legs (legs 2-5) are flattened, and the chelipeds and walking legs have long, plumose setae along the margins (photo).  The tips of its dactyls on legs 2-5 are only slightly curved (photo), and the propodus of these legs is about the same length as the dactyl (photo).  The inner margin of the dactyl of its claw has a distinct tooth (photo).  Color is variable.  Carapace color is dappled dark brown or black, red-brown and greenish-brown on white and ivory or yellow.  All the carapace margins except the posterior one have a lighter border.  The chelipeds and walking legs are pale yellow with greenish-brown patches, which are reticulated on the carpus and propodus.  The abdomen is lighter in color (photo). Carapace width to 8 mm for females, 6.5 mm for  males.

How to Distinguish from Similar Species: P. occidentalis and P. schmittii have carapaces more than 2x as wide as long and with pointed lateral margins, plus have no tooth on the inner margin of the dactyl of their chela. P. tubicola has a propodus longer than the dactyl on legs 3-5 and lives in Terebellid tubeworm tubes.  Pinnixa faba and P. littoralis have strongly curved tips to their dactyls and usually live commensally in bivalves.

Geographical Range:  Queen Charlotte Islands, BC, Canada to Puget Sound

Depth Range:  Intertidal

Habitat:  Commensal in lugworm burrows.

Biology/Natural History:   This species is not often collected.


 
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References:

Dichotomous Keys:
  Coffin, 1952
  Kozloff, 1987, 1996

General References:
  Hart, 1982
  Ricketts et al., 1985

Scientific Articles:

Web sites:

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

Chelipeds
This closeup of the chelipeds shows the tooth on the inner margin of the dactyl
 


Legs
The legs are flattened, translucent with darker spots or reticulations, and are fringed with long, abundant plumose setae.  It can also be seen that the dactyls and the propodus of the walking legs are of approximately equal length (though the dactyls are mostly extended downward in this photo and may appear shorter), and that the dactyls are nearly straight.  Notice that the last leg is much shorter than the others.
 


Female abdomen
This view of the underside shows how much lighter the abdomen is, and also reveals that this individual is a female.


Authors and Editors of Page:
Dave Cowles (2009):  Created original page
CSS coding for page developed by Jonathan Cowles (2007)