This small cancer crab has
a dark tip to its claw, the dorsal surface is covered with low tubercles,
and the legs have many setae
The dorsal surface of
of the chelipeds
have prominent tubercles
but no spiny ridges (picture).
to 5 cm, and is more nearly circular in outline than seen in other
crabs (the anterolateral
margins do not meet at an angle, as they do in other cancer
Usually a dull red as above but may be lighter in color (picture).
Underside is usually white.
(Dana), Schweitzer and Feldmann, 2000)
Common name(s): Pygmy rock
crab, Hairy cancer crab, Oregon
cancer crab, Oregon rock crab
Trichocera oregonensis, Platycarcinus recurvidens, Trichocarcinus
Trichocarcinus recurvidens, Trichocarcinus walkeri
Numbers on scale are centimeters.
|(Photo by: Dave
Cowles, July 2005)
How to Distinguish
from Similar Species: Glebocarcinus
branneri is also small but has spiny ridges and no tubercles
on the chelae;
plus is not as common. Lophopanopeus
bellus is similar size and shape, is found in
similar areas, and
has black claw tips and an oval carapace
but does not have the 5 teeth between the eyes characteristic of Cancer
crabs, plus its carapace
is often an off-white.
Note: Species formerly in genus Cancer
have been recently subdivided into several genera (Ng
et al., 2008; Schweitzer
and Feldmann, 2010). Of our local genera, Cancer,
have a carapace
wider than long plus only scattered setae
on the carapace
margins and legs while Glebocarcinus
has a carapace of approximately equal length and width, often with
regions and with setae
along the edges; and setae on the outer surface of the chela
as well as on the legs. Metacarcinus
can be distinguished from Cancer
carapace teeth which are distinct and sharp plus the male has a rounded
tip to the telson, while Cancer
teeth which are low and lobed, separated by deep fissures plus the male
has a sharply pointed telson (Schram
and Ng, 2012). Romaleon
can be distinguished from Cancer
because it has a distinct tooth on the anterior third of the posterolateral
margin of the carapace
while the other two genera do not.
Range: Pribilof Islands to
Palos Verdes, CA; uncommon S of Pt. Arena, CA. Common in the
but not common in the southern part of its range.
Depth Range: Intertidal
to 436 m
nestles in small holes such
as dead barnacles and under rocks (photo).
Often uses its rounded carapace to block the entrance to the hole.
This crab is very
common in the intertidal zone in small spaces under and between rocks,
and also subtidally in dead barnacles. It emerges at night to
mainly on small barnacles, but also on snails, bivalves, worms, and
green algae. Is an important predator on small Japanese
gigas. Males have larger chelipeds than
Predators include pacific cod, and occasionally river otter and red
crab Cancer productus. May be found in
"harems" of one male
and several females in their crevices, especially during the summer
Mating takes place after
the females molt, and the males often carry females who are preparing
molt, and afterward until she has hardened. Ovigerous females
found in Puget Sound from November to April/May. May be
by parasitic sacculinid
barnacles. When disturbed outside its hole, this
crab may fold
its legs and roll like a stone.
to Main Page
and Fairbanks, 1966
and Carlton, 1975
and Snook, 1955
and McConnaughey, 1985
et al., 1980
and O'Clair, 1998
et al., 1985
D. Guinot, and P.J.F. Davie, 2008. Systema
I. An annotated checklist of extant brachyuran crabs of the
Raffles Bulletin of Zoology, Supplement 17 pp. 1-286 (Clicking on link
will load a pdf of the long article)
Frederick R. and Peter K.L. Ng, 2012. What is
of Crustacean Biology 32:4 pp. 665-672
C.F. and R.M. Feldmann, 2000. Re-evaluation of the
Latereille, 1802 (Decapoda: Brachyura) including three new genera and
new species. Contributions to Zoology 69:4 pp.
General Notes and
Observations: Locations, abundances,
Some individuals are lighter colored, as this individual.
on scale are centimeters. Photo by Dave Cowles, July 2005.
Front-on view. Note the tubercles on the dorsal margins of
The many setae are most evident when the animal is underwater, as in
This species often nestles in holes in rocks, as seen in this photo
from Cape Flattery, WA. Often a male and female nestle in the
hole, or in two nearby holes.
Two individuals are nestling in adjacent holes (top
right and bottom
left) in this intertidal rock at Beach #4, Kalaloch. The
hole is also occupied by an anemone. Photo by Dave Cowles,
|Some Glebocarcinus oregonensis,
especially larger and deepliving
individuals, seem to have a very pronounced pattern clusters of raised
tubercles on the carapace.
This individual was caught at 100 m depth in the San Juan Channel.
||Here is a closeup of the two patches of tubercles
from the individual
to the left, just behind the head. The tubercles appear to be
integral part of the exoskeleton but are sharply raised above
As a whole, the size and shape of the individual tubercles reminds me
the bumps present on the large chelae of the lithodid crab Oedignathus
inermis. I wonder whether they are simply
of the carapace
or actual thickenings, and whether they may function to make the
stronger and more crush-proof.
I found this individual in the Rosario Seawater reservoir tank before
the seawater system was turned on in June 2016. To get there,
would have had to have passed through the seawater intake screens as a
larve less than 1 mm in diameter in summer 2015. At the end
summer it would have been settled in the bottom 5-10 cm of water in the
tank when the rest of the tank was drained at the end of
From that time until summer 2016 it would have survived over 9 months
the total darkness of the tank, in 5-10 cm of water with 1-2 cm of silt
on the bottom. Carapace width 3.5 cm. The barnacle
on the crab's
carapace is alive as well. Photo by Dave Cowles, June 2016.
This female found in the intertidal is so heavily 'berried' (full of
eggs, which are carried on her pleopods on the abdomen) that her
cannot be folded up under her thorax, as crabs usually do. Photo by
Cowles, July 2017
Authors and Editors of Page:
Dave Cowles (2005): Created original page