Oedignathus inermis (Stimpson, 1860)
Common name(s): Paxillose crab, Granular claw crab, Soft-bellied crab
|Synonyms: Hapalogaster inermis, Hapalogaster brandti, Oedignathus gilli|
|Oedignathus inermis from Sares Head. Found intertidally in a sea cave|
|(Photo by: Dave Cowles, August 2007)|
How to Distinguish from Similar Species: Of the Lithodid crabs with soft abdomens, Placetron wosnessenskii has a much thinner abdomen and has scales on the carapace and legs. Acantholithodes hispidus has large spines on the rostrum. Hapalogaster mertensii and H. grebnitzkii have strongly flattened cephalothorax and legs and have spines on the upper surface of their chelipeds.
Geographical Range: Amchitka Island, AK to Monterey, CA; eastern Russia, Japan, Korea. Mostly on the open coast. Rarely seen in the San Juan islands and is said to not to occur in Puget Sound; rare in California.
Depth Range: Middle intertidal to 15 m
Habitat: Under encrusting coralline algae, under Mytilus californianus mussels or Anthopleura xanthogrammica anemones, in crevices, and in other protected areas
Biology/Natural History: These
crabs are often found in pairs, and may be in such a tightly secluded space
that they appear to be trapped. They feed by straining plankton from
the water with their third maxillipeds.
Captive individuals also catch worms and small crustaceans with their small
claw and crush mussels with the large claw. Predators include black
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Johnson and Snook, 1955
Morris et al., 1980
O'Clair and O'Clair, 1998
General Notes and Observations: Locations,
abundances, unusual behaviors:
The abdomen of this species is thick and soft. The basal segment and the two distal segments have some calcified plates, which are not evident in this view.
One claw is much larger than the other. The "palm" of the chela on the large claw is longer than the dactyl. The upper surface of the chelipeds is covered with prominent, granular tubercles but with no obvious spines.
The rostrum is short. The carapace has orange-red tubercles with a white spot in the middle.
The walking legs have setae and granules but no spines.