This large Cancer crab has
a dark tip to its claws (photo).
surface of the carapace is nearly smooth or only slightly rough, but
not have rough tubercles or setae. The carapace is at least
as wide as long and frequently exceeds 6 cm. The ventral
of living individuals has red spots on a pale yellow background, and
dorsal surface is purplish red. The undersurface of the carapace also
setae, as does the dorsal surface of young ones (but not
Carapace usually up to about 13 cm wide but may be up to 15 cm. The
has 11 anterolateral teeth and is widest at the 8th tooth. Some of the
teeth curve forward.
Romaleon antennarium (Stimpson),
Schweitzer and Feldmann, 2000
Common name(s): Pacific rock crab,
Common rock crab, Spot-bellied
rock crab, Rock crab, Red rock crab
|Romaleon antennarius, preserved
specimen collected in California.
|(Photo by: Dave Cowles May
How to Distinguish from
This is one of the two large local Cancer crabs with black tips on
chelae. The other, Cancer productus,
has a rough dorsal surface on its carapace and a few tubercles and has
no ventral red spots. Its carapace is also produced forward
the eyes. Other Cancer crabs with black chelae, such as Glebocarcinus
oregonensis, have a tuberculate carapace which is
than 6 cm wide and is not 1.5x or more as wide as long.
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
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
to Cabo San Lucas, Baja California but rarely seen north of Coos Bay,
(But common in Barkley Sound on Vancouver Island)
Intertidal to 91 m, usually
less than 45 m.
Common in the low rocky intertidal.
Often found under rocks, sometimes partly buried in sand under the
Subtidally may be on gravel bottoms or in kelp beds.
on the exposed coast.
scavenged bits and animals such as Tegula funebralis and hermit
It captures the hermit crabs by gradually chipping away the edges of
hermit's shell until the hermit crab has nowhere else to
harvested by humans for crab legs. In California, become
about 2 years. Berried (egg-carrying) females are most often
November to January. The young have vivid color patterns on
similar to those of C. productus young. Most active at night.
and Carlton, 1975
and Rokop, 1985
and Snook, 1955
and McConnaughey, 1985
et al., 1980
et al., 1985
General Notes and
Observations: Locations, abundances,
The claws of Romaleon antennarius are tipped in
Photo of a preserved specimen by Dave Cowles
Authors and Editors of Page:
Dave Cowles (2007): Created original page