|Female C. gracilis found on the Evergreen beach, Olympia, Washington.|
Slender Crab, Graceful Crab
Cancer gracilis or more commonly known as 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) . Cancer gracilis has been caught from Alaska to Bahía Magdelena, Baja California . Although C. gracilis is only found in the Pacific Ocean, it has cousins in the Atlantic Ocean.
Often mistaken for a Dungeness Crab, C. magister, it can be distinguished from its much larger relative by the shape of its carapace (which is widest at the ninth tooth instead of the tenth), the white edging of the carapace teeth, and the lack of the serrations on the upper margin of the claws . The tops of the claws are sharp-edged, with two or three prominent teeth. The last three joints of all the walking legs are hairless. Compare particularly the last three joints of the last pair of legs with those of the Dungeness crab, the only other crab of this group which has white-tipped pincers. Since the slender crab seldom exceeds a width of 3 inches across the back, it can only be confused with the young of the Dungeness crab .
The abdomen, or tail flap, which is folded closely against the underside of the crab, is much broader in the female than in the male crab; the tip of the last segment of the tail flap is pointed in both male and female [SOURCE] This broad tail flap is necessary in the female to accommodate at spawning time the huge numbers of eggs that are attached and receive protection between this flap and the body until hatched. In the adult stage, the comb-like fringe of hair around the edges of the tail flap is quite long in the female but rather short and hardly noticeable in the male.
Distribution & Habitat
Primarily subtidal on sandy or muddy substrate preferring slightly muddier areas than C. magister, though it cannot tolerate low salinity water so it is usually absent from estuaries. Recorded from the lower intertidal to 143 m (470ft) .
Life Cycle & Ecology
This species is a scavenger, or eats small invertebrates. Predators include staghorn sculpin, starry flounder, the seastar Astropecten verrelli, and the giant octopus Enteroctopus dofleini .
Females in all reproductive conditions aggregate in relatively small areas, where mating activity appears most intense, and play an active role in mating, often initiating interactions with the prospective male partner. Females usually are found buried in the mud. Maximum mating activity has been observed towards the end of the spawning/hatching season (August). In Puget Sound the eggs were borne from December to April. Males protect females after mating. Megalopae and juveniles often cling to large jellyfish such as Pelagia colorata .
- ↑ Eugene N. Kozloff (1993) Seashore Life of the Northern Pacific Coast. Seattle: University of Washington Press.
- ↑ Trisha Towanda & Erik V. Thuesen (2006). Ectosymbiotic behavior of Cancer gracilis and its trophic relationships with its host Phacellophora camtschatica and the parasitoid Hyperia medusarum. Ecology Progress Series 315: 221–236. [Main Article]
- ↑ Jensen, Gregory C. Pacific Coast Crabs and Shrimps. Sea Challengers, 1995, p. 28.
- ↑ http://www.nwmarinelife.com/htmlswimmers/c_gracilis.html
- ↑ http://www.dfg.ca.gov/marine/dungeness_crab.asp#slender
- ↑ http://seanet.stanford.edu/Crustacea/index.html#Cancer_gracilis
- ↑ McGaw Iain J (2006). Feeding and digestion in low salinity in an osmoconforming crab, Cancer gracilis I. Cardiovascular and respiratory responses. Journal of Experimental Biology 209: 3766-3776.[Main Article]
- ↑ J. M. Orensanz et al. (1995). The breeding ecology of Cancer gracilis (Crustacea: Decapoda: Cancridae) and the mating systems of cancrid crabs. Journal of Zoology.235:411-437 [Main Article]
- ↑ http://www.wallawalla.edu/academics/departments/biology/rosario/inverts/Arthropoda/Crustacea/Malacostraca/Eumalacostraca/Eucarida/Decapoda/Brachyura/Family_Cancridae/Cancer_gracilis.html
Eales, Phillip et al. Oceans: The World’s Last Wilderness Revealed. DK ADULT; First American Edition, October 16, 2006, p. 123 [ISBN-13: 978-0756622053]
Harrison Michelle K and Crespi Bernard J (2002). Phylogenetics of Cancer Crabs (Crustacea: Decapoda: Brachyura). Molecular Phylogenetics and Evolution, 12:186-199. Main Article