Cancer gracilis

Taxobox
name = "Cancer gracilis"


image_width = 250px
image_caption = "Cancer gracilis" caught in Southern California
regnum = Animalia
phylum = Arthropoda
subphylum = Crustacea
classis = Malacostraca
ordo = Decapoda
subordo = Pleocyemata
infraordo = Brachyura
familia = Cancridae
genus = "Cancer"
species = "C. gracilis"
binomial = "Cancer gracilis"
binomial_authority = Dana, 1852

"Cancer gracilis" or more commonly the "graceful rock crab" or "slender crab" is one of only two members of the genus "Cancer" whose chelae (claws) are white tipped, the other crab being "C. magister" (Dungeness crab). [Kozloff, E. N. (1993) "Seashore Life of the Northern Pacific Coast". Seattle: University of Washington Press.] "Cancer gracilis" has been caught from Alaska to Bahía Magdelena, Baja California. [Nations, J. D. (1975) The genus "Cancer" (Crustacea: Brachyura): Systematics, biogeography and fossil record. "Natural History Museum of Los Angeles County Science Bulletin" 23: 1-104.] Although "C. gracilis" is only found in the Pacific Ocean, it has cousins in the Atlantic Ocean. The genus "Cancer" apparently evolved in the Pacific Ocean and later migrated to the Atlantic Ocean. [Harrison, M. K. & Crespi, B. J. (1999) Phylogenetics of "Cancer" Crabs (Crustacea: Decapoda: Brachyura). "Molecular Phylogenetics and Evolution" 12: 186-199.] Larvae and small juveniles of this species are often seen riding jellyfish, especially "Phacellophora camtschatica". The juvenile crabs steal food from the jellyfish and also clean off parasitic amphipods. [Towanda, T. & Thuesen, E. V. (2006) Ectosymbiotic behavior of "Cancer gracilis" and its trophic relationships with its host "Phacellophora camtschatica" and the parasitoid "Hyperia medusarum". "Marine Ecology Progress Series" 315: 221-236.]

Morphology

Like the other members of the family Cancridae, the "slender crab" has a very broad and oval carapace with dull tooth-like protrusions toward the front of the carapace. Female crabs can be distinguished from male by the broad tail flap on their undersides, which are used for protecting their eggs when they are gravid. The slender crab usually has a carapace that is olive brown and legs that vary from yellowish brown to purple. "C. gracilis" only grows to a width of about 3½ inches and so resembles a juvenile "C. magister". Often the two species can be confused as "C. gracilis" looks very similar to a juvenile Dungeness crab. They can readily be distinguished from each other however by the appearance of hair on the posterior three legs of "C. magister" where "C. gracilis" is almost always hairless. Another telling characteristic of the slender crab is that the last segment of its tail flap is pointed, where "C. magister" is curved.

References