Glebocarcinus oregonensis (Dana), Schweitzer and Feldmann, 2000) Common name(s): Pygmy rock crab, Hairy cancer crab, Oregon cancer crab, Oregon rock crab
Synonyms:  Cancer oregonensis, Trichocera oregonensis, Platycarcinus recurvidens, Trichocarcinus oregonensis, Trichocarcinus recurvidens, Trichocarcinus walkeri
Phylum Arthropoda  Subphylum Crustacea   Class Malacostraca    Subclass Eumalacostraca     Superorder Eucarida      Order Decapoda       Suborder Pleocyemata        Infraorder Brachyura         Family Cancridae
	Glebocarcinus oregonensis.  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, Romaleon, and Metacarcinus 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 because Metacarcinus 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 and Metacarcinus 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 Islands to Palos Verdes, CA; uncommon S of Pt. Arena, CA.  Common in the north but not common in the southern part of its range.

Depth Range: Intertidal to 436 m

Habitat: Often nestles in small holes such as dead barnacles and under rocks (photo).  Often uses its rounded carapace to block the entrance to the hole.

Biology/Natural History: 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 feed mainly on small barnacles, but also on snails, bivalves, worms, and some green algae.  Is an important predator on small Japanese oysters Crassostrea gigas.  Males have larger chelipeds than do females.  Predators include pacific cod, and occasionally river otter and red rock crab Cancer productus.  May be found in "harems" of one male and several females in their crevices, especially during the summer breeding season (photo).  Mating takes place after the females molt, and the males often carry females who are preparing to molt, and afterward until she has hardened.  Ovigerous females are found in Puget Sound from November to April/May.  May be infected by parasitic sacculinid barnacles.  When disturbed outside its hole, this crab may fold its legs and roll like a stone.

References:

General References:
Harbo, 1999
Jensen, 1995
Johnson and Snook, 1955
Kozloff, 1993
McConnaughey and McConnaughey, 1985
Morris et al., 1980
Niesen, 1997
O'Clair and O'Clair, 1998
Ricketts et al., 1985
Sept, 1999

Scientific Articles:

Burnett, Nicole, 2024: A practical identification guide to the zoeae of the invasive European green crab, Carcinus maenas (Linnaeus, 1758) (Decapoda: Brachyura: Carcinidae), and to the zoeae of the families of brachyuran crabs in Washington state, USA. Journal of Crustacean Biology 44:4.  doi.org/10.1093/jcbiol/ruae064

Ng, P.K.L., D. Guinot, and P.J.F. Davie, 2008.  Systema Brachyurorum: part I.  An annotated checklist of extant brachyuran crabs of the world.  Raffles Bulletin of Zoology, Supplement 17 pp. 1-286

Schram, Frederick R. and Peter K.L. Ng, 2012.  What is Cancer?  Journal of Crustacean Biology 32:4 pp. 665-672

Schweitzer, C.F. and R.M. Feldmann, 2000.  Re-evaluation of the Cancridae Latereille, 1802 (Decapoda: Brachyura) including three new genera and three new species.  Contributions to Zoology 69:4 pp. 223-250 

Some individuals are lighter colored, as this individual.  Numbers on scale are centimeters.  Photo by Dave Cowles, July 2005.

Front-on view.  Note the tubercles on the dorsal margins of the chelipeds

The many setae are most evident when the animal is underwater, as in this picture.

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 same hole. 

Two individuals are nestling in adjacent holes (top right and bottom left) in this intertidal rock at Beach #4, Kalaloch.  The bottom left hole is also occupied by an anemone.  Photo by Dave Cowles, July 2012. 
 

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 an integral part of the exoskeleton but are sharply raised above it.  As a whole, the size and shape of the individual tubercles reminds me of the bumps present on the large chelae of the lithodid crab Oedignathus inermis.  I wonder whether they are simply raised portions 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 reservoir 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.