This grapsid crab (rectangular
wide-set eyes and no teeth on the carapace between, no rostrum)
is a common intertidal crab. The merus
of legs 2-5 is not flattened. The dorsal surface of the
does not have transverse ridges or lines, and is variously colored,
with light greenish spots on a dark reddish-brown background, but may
a pale green (photo),
or even nearly white (photo).
There are 3 teeth
on the anterolateral margin of the carapace (photo).
The legs have abundant
and the chelipeds
have no purple spots (photo),
but have yellow
or white on the tips. Carapace width to 34.7 mm in males and
mm in females.
Hemigrapsus oregonensis (Dana,
Common name(s): Yellow shore
Mud-flat crab, Oregon shore
crab, Hairy shore crab, Green shore crab
Brachyura (true crabs)
|Hemigrapsus oregonensis from
|(Photo by: Dave
How to Distinguish
Similar Species: Pachygrapsus
crassipes, which lives mostly farther south, has
on the dorsal surface of its carapace and 2 teeth on the anterolateral
margin of the carapace. Hemigrapsus
nudus has few or no setae on the legs and purple
spots on the chelipeds.
The first zoeal stage of H. oregonensis
can be distinguished from zoeae of H.
nudus because H. oregonensis
has lateral projections on only abdominal segment 2 while H.
nudus has lateral projections on abdominal
segments 2 and 3
to Bahia de Todos Santos, Baja California.
Depth Range: (mainly
mud flats, algal mats and
eelgrass beds, in bays and estuaries and on open beaches where there is
plenty of fine sediment.
This species is
a better osmoregulator than the other local shore crabs (H.
nudus), which is probably associated with its being more
estuaries. It also often digs burrows and is capable of
more hypoxic conditions than the other shore crabs are. Feeds
at night, mostly on diatoms and green algae, but will eat meat if it
opportunity. Predators include shorebirds. May have
isopod Portunion conformis in the perivisceral
cavity (not evident
and Fairbanks, 1966
and Carlton, 1975
et al., 1980
et al., 1985
Seok Hyun and Hyun Sook Ko, 2008. First zoeal
stages of six species
Brachyura: Grapsidae) from the northern Pacific including an
key. Journal of Crustacean Biology 28:4 pp. 675-685
General Notes and
Observations: Locations, abundances,
The chelae in this species does not have purple spots, as does H.
The legs of H. oregonensis have setae, as visible
View of the underside of a female (left) and a male (right).
Note the broader, more rounded abdomen on the female and the narrower,
pointed abdomen on the male.
|Below is another series of dorsal and ventral
views of a male Hemigrapsus
oregonensis. Notice how narrow the abdomen is in the
ventral view, and that they have a very limited number of pleopods on
the abdomen, used for transferring sperm duing fertilization.
||Below is another series of dorsal and ventral
views of a female Hemigrapsus oregonensis. Notice in the ventral view
that their abdomen is much broader than the male's. They have a series
feathery pleopods on their abdomen, used for carrying the eggs while
they are brooding them.
Closeup of the underside of the abdomen of a female. Females
in brachyuran crabs have pleopods on their abdomens which function to
View of the underside of a male Hemigrapsus oregonensis.
Male brachyuran crabs have no pleopods on their abdomen except for two
hemipenes used for transferring sperm.
The right chela of a male. There is a tuft of setae on the
of the chela on males.
This crab has many color variations. A common form is a white
or nearly white carapace, as seen in this individual. Photo
Cowles, July 2005
Light green is another common color. Photo by Dave Cowles,
This individual from Kalaloch also shows the hairy legs (actually setae
not hairs) common on this species, plus the three teeth on the
margin of the carapace
which distinguish genus Hemigrapsus from Pachygrapsus
crassipes (which has only two teeth).
Although abundant setae
on the legs is characteristic of H. oregonensis and
in this individual, most individuals found near the Rosario Marine Labs
have very few setae
on the legs.
Photo by Dave Cowles, July 2009
Authors and Editors of Page:
Dave Cowles (2005): Created original page