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).
Width of carapace
to 5 cm, and is more nearly circular in outline than seen in other
crabs (the anterolateral and posterolateral margins do not meet at an
as they do in other cancer crabs). Usually a dull red as
may be lighter in color (picture).
is usually white.
Schweitzer and Feldmann, 2000)
Common name(s): Pygmy rock
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
How to Distinguish
Similar Species: Glebocarcinus
branneri is also small but has spiny ridges and no tubercles
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
Note: Species formerly in genus Cancer have been
subdivided into several genera (Ng
et al., 2008; Schweitzer
and Feldmann, 2010). Of our local genera, Cancer, Romaleon,
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
granular 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
has anterolateral carapace teeth which are distinct and sharp plus the
male has a rounded tip to the telson, while Cancer
has anterolateral carapace 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.
Geographical Range: Pribilof
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
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.
and Fairbanks, 1966
and Carlton, 1975
and Snook, 1955
and McConnaughey, 1985
et al., 1980
and O'Clair, 1998
et al., 1985
P.K.L., D. Guinot, and P.J.F. Davie, 2008.
Systema Brachyurorum: part I. An annotated checklist of
brachyuran crabs of the world. Raffles Bulletin of Zoology,
Supplement 17 pp. 1-286 (Clicking on link will load a pdf of the long
Frederick R. and Peter K.L. Ng, 2012. What is
Cancer? Journal of Crustacean Biology 32:4 pp. 665-672
C.F. and R.M. Feldmann, 2000.
Re-evaluation of the Cancridae Latereille, 1802 (Decapoda: Brachyura)
including three new genera and three new species.
to Zoology 69:4 pp. 223-250
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
individuals are nestling in adjacent holes (top right and bottom left)
in this intertidal rock at Beach #4, Kalaloch. The bottom
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
in the San Juan Channel.
||Here is a closeup of the two patches of tubercles
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 exoskeleton stronger and more crush-proof.
I found this individual in the Rosario Seawater
tank before the seawater system was turned on in June 2016.
To get there, it 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 of that 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 summer. From that time until summer
2016 it would have survived over 9 months in 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.
Authors and Editors of Page:
Dave Cowles (2005): Created original page