Description:
As a Lithodid crab,
this species has no uropods
and the abdomen is folded against the underside of the thorax.
Its 5th walking legs are reduced. Oedignathus
inermis has a thick, soft abdomen which is not tightly
held under
the thorax (photo).
The first (basal) segment
of the abdomen has calcified plates, as do the two terminal
ones. Oedignathus
inermis has chelipeds
very unequal in size (the right cheliped
is largest) and the dactyl
is shorter than the "palm" of the propodus.
The rostrum
is sharp but has no spines (photo).
The legs
are rounded (not heavily flattened). The chelipeds
have large granular tubercles
but no spines on the upper surface. The large cheliped
has violet to gray or blue tubercles
and a smooth tan to white tip to the claw with a spoonlike hollow where
the propodus
and dactyl
contact one another. The shall cheliped
has small, sharp granules and setae.
The walking legs have sharp granules, setae,
and dark brown and white spots (photo).
The anterior
margins of legs 2-4 have some setae,
tubercles,
and small spines but no large spines. Note, however, that there are
large
spines on the anterior margins of leg 1 (the chelipeds).
Carapace
to 3 cm long and 2.5 cm wide in males, 2 cm wide in females; wider
posteriorly
than anteriorly, brown with scales on the dorsal surface. It
has
white-centered orange granules and dark brown spots, but these colors
may
be masked by mud. May have white on the sternum.
There are
few if any setae
on the body.
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
oystercatchers.
References:Dichotomous Keys:Coffin, 1952 Hart, 1982 Kozloff 1987, 1996 Smith and Carlton, 1975 Wicksten, 2009 General References:
Scientific Articles:
Web sites:
General Notes and
Observations: Locations,
abundances, unusual behaviors:
Authors and Editors of Page: Dave Cowles (2007): Created original page CSS coding for page developed by Jonathan Cowles (2007) |