This subtidal hermit
crab, like most local hermit crabs has a smooth carapace
which is only partly calcified and the bases of the eyescales
are not covered by the carapace
The abdomen is curved.
of the right cheliped
is longer than wide and is not extremely flattened (photo).
do not have a deep median furrow and they terminate in a single spine(photo).
of legs 2 and 3 are not striped and are not obviously twisted in
to the propodus
The dorsal surface of
the palm (propodus)
of the left chela
does not have a prominent ridge or crest near the midline.
surface of the merus
of the right cheliped
does not have prominent tubercles(photo).
The left chela
is more elongated than triangular (photo),
is longer than the merus,
and there is a single row of large spines on the eminence near the
surface of the propodus.
The carpus of the right cheliped
is about 1.5x as long as wide. The rostrum
is pronounced and sharp tipped. There is a distinct white
the distal parts of the merus
of the chelipeds
(photo), which is the
source of the animal's common
name. The dorsal carapace has a network of white, tan,
and red with a red margin. The flagellum of the second
reddish-brown with some white. There is no tuft of setae
on the dorsal side of the base of the cornea
Pagurus dalli (Benedict, 1892)
Common name(s): Whiteknee hermit
dalli, from about
20 m depth at Mukilteo. The "shell" on its back is composed
of a colony of Hydractinia
|(Photo by: Dave
How to Distinguish
Similar Species: Pagurus
stevensae has a right cheliped
more triangular than elongate and a double row of spines on the
near the midline of the dorsal surface of the propodus
of the left chela,
plus it has no white band on the end of the merus
of its chelipeds. Pagurus
kennerlyi has a white band on the merus
of the chelae
but its second antennae have alternating light and dark bands and it
a tuft of setae
on the dorsal side of the base of its cornea.
Sea to Oregon; widespread but not abundant.
Very low intertidal
to 276 m
Gravel, sandy, or mud
bottoms; symbiotic with sponges (or hydroids)
is said to generally live symbiotically with the sponge Suberites
latus or Suberites
which dissolves and overgrows its shell. This specimen was in
made largely or entirely of the hydroid Hydractinia
milleri. This hydroid is said to
encrust shells which
have hermit crabs living in them, and eventually to overgrow the shell
as the crab grows. The hermit crab frequently rubs
of its second antennae over the hydroid colony. In
crab symbiosis this behavior was found to result in the hermit crab
and eating some of the plankton the Hydractinia
The presence of Hydractinia
on a hermit crab seems to at least partially deter predation by
Octopus usually readily capture hermit crabs and other
However, an octopus clearly thinks twice about attacking a hermit crab
on its shell.
here for a movie showing how octopus deal with Hydractinia-covered
and Fairbanks, 1966
et al., 1985
General Notes and
abundances, unusual behaviors:
I have rarely encountered and identified this
species. I can find
no references in the literature to its living symbiotically with a
(though it lives in a similar manner with sponges). My thanks
Kirt Onthank for his sharp-eyed viewing during a dive which resulted in
finding this symbiotic pair.
In this side view the slight coiling of the "house" is
house is made of the hydroid Hydractinia
milleri. The egglike structures are
gonozooids of the hydroid.
The hermit crab gives no sign of being stung by the hydroid.
other species of hermit crabs, known to be symbiotic with Hydractinia,
also do not seem to be vulnerable to their sting while some other
crab species are.
This dorsal view of the head shows the smooth carapace,
the lack of tufts (setae) on the dorsal margin of the cornea,
and the fully exposed eyescales
with a single terminal spine and no median dorsal furrow.
of the left chela
is longer than the merus.
of the right chela
is about 1 1/2 times as long as wide and is not extremely flattened
is the last segment visible on the right chela
here, as the propodus
are folded underneath as the animal crawls along). The merus
of both chelae
has a prominent white band on the terminal end.
The 2nd and 3rd dactyls
are not striped, do not have ventral spines, and are not obviously
in relation to the propodus.
This is a view of the merus
(top right, spiny), carpus (spiny), propodus,
of the right second leg.
This ventral view of the right cheliped
shows that the ventral side of the merus
(to the left of the sharp turn, or "knee") does not have any prominent
This X-ray view of the above live animal shows that there is a small
gastropod shell at the base of the Hydractinia
house. The shell is about 5 mm long.
Digital X-ray compliments of Julie Kellogg, DDS and Tietan Dental
Authors and Editors of Page:
Dave Cowles (2007): Created original page
CSS coding for page developed by Jonathan Cowles (2007)