Description: As with all Cancer crabs,
this species has 5 teeth between the eyes. Its carapace
is widest at the 9th tooth lateral to the eyes, and behind this point there
is a distinct 10th tooth. The tips of the chelae
are white (photo), and there are no spiny ridges
on the carpus,
of the chelae
(although there are two blunt teeth on the dorsal ridge of the propodus)
(photo). The carapace
is slightly convex dorsally. The dactyls
of the pereopods
(walking legs) are cylindrical. The dorsal surface of the upper part
of the legs is purple in many individuals. Carapace
width to 11.5 cm (males) or 10.6 cm (females) but usually not over 6 cm.
Metacarcinus gracilis (Dana, 1852) Schweitzer and Feldmann, 2000
Common name(s): Graceful rock crab, Graceful crab, Slender
|Synonyms: Cancer gracilis
|Metacarcinus gracilis, about 5 cm carapace
width, from 100 m depth, San Juan Channel
|(Photo by: Dave Cowles, July 2006)
How to Distinguish from Similar Species:Metacarcinus
magister has a carapace
widest at the 10th tooth, with no teeth behind that point, and also has
spiny ridges on the carpus, propodus,
of the chela.
It also has more flattened dactyls
on the pereopods
and the dorsal surface of the upper parts of the legs is not purple.
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
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).
Geographical Range: Prince William
Sound, Alaska to Baja California, Mexico
Depth Range: Intertidal to 174 m
Habitat: Mainly subtidal on sand and
mud, sometimes near eelgrass beds. May be on pilings.
Biology/Natural History: 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 usually are found buried in the mud.
Seasonally found in bays but cannot osmoregulate and does not tolerate
brackish conditions. In Puget Sound eggs were borne from December
to April. Males protect females after mating. Megalopae and
juveniles often cling to large jellyfish such as Pelagia colorata.
and Fairbanks, 1966
and Carlton, 1975
and Snook, 1955
et al., 1980
and O'Clair, 1998
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.
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
General Notes and Observations: Locations, abundances,
The tips of the chelae
are white. There are no spiny ridges on the carpus,
of the chelae,
though there are two spines or tubercles
on the dorsal ridge of the dactyl.
The appendages seen covering the mouth are the maxillipeds,
which are found in all crabs. The white objects between the maxillipeds
are the hardened tips of the mandibles.
|This female C. gracilis, 8.5 cm carapace
width, was found at March Point. She appears to be gravid (carrying
eggs). The eggs, however, are much smaller and dirtier-looking than
crab eggs usually are, leading me to suspect that she may be parasitized
by a rhizocephalan sacculinid barnacle. However, the "eggs"
did not form a sac-like structure as usually seen in rhizocephalans.
|Raising the abdomen shows the dark gray and black mass of eggs.
The female was docile and made little attempt to escape or to pinch.
|A view through the microscope shows the mass is composed of a large
number of tiny, slightly flattened, egg-like objects attached to her pleopods.
Note the tip of her chela
at the top right for size. I will have to watch for more gravid females
to see whether these tiny, dirty-looking eggs are the norm for Cancer
gracilis. Photos by Dave Cowles July 2007
This view of a Padilla Bay crab shows the purple legs seen in many
individuals. Photo by Dave Cowles July 2008
This squeak-clean individual I found in the Rosario Seawater System
reservoir tank before starting up the seawater system in June 2016.
To get there, the crab would have had to pass through the intake filter
(maximum clearance 1 mm) the previous summer, be pumped up the hill to
the reservoit, remain in the tank 5-10 cm of water in the bottom of the
tank while the rest of the water drained out at the end of the summer,
and then survive and grow to this size in the perhaps 1-2 cm deep coating
of silt on the bottom of the tank in total darkness for over 9 months
until we opened the seawater system again. No doubt the crab is so
clean because it has never had to deal with algal overgrowth in the darkness.
width is 4 cm.
Authors and Editors of Page:
Dave Cowles (2006): Created original page