Porcelain crabs are Anomuran
crabs, as can be seen by the antennae being lateral to the eyes, the
last leg (picture), and
the fact that the abdomen
is not held tightly against the underside of the thorax. The
of Petrolisthes has uropods.
eriomerus has a carpus
about 2x as long as wide and with parallel anterior and posterior
The outer edge of the palp
of the maxilliped
is bright blue, and there is also blue on the cheliped.
Overall color brown to gray-blue. Carapace length up to 1.9
roughness and granulations on the anterior part. Chelae
are usually nearly equal in size and strongly flattened.
flagellum is grayish green.
Petrolisthes eriomerus Stimpson, 1871
Common name(s): Flattop crab,
|Petrolisthes eriomerus collected
from Sares Head. Carapace
width 1.3 cm
|(Photo by: Dave Cowles
June 26, 2005)
How to Distinguish from
Similar Species: Petrolisthes
cinctipes has a shorter carpus
and the margins are not parallel, plus the palp
of its maxilliped
is orange red. Pachycheles crabs such as Pachycheles
rudis have much thicker chelae
Geographical Range: Chicagof
to La Jolla, CA
Depth Range: Low
intertidal to 86 m; primarily
intertidal from central CA southward.
rocks, on both exposed coasts
and protected water. Also on kelp holdfasts and in mussel
Most common in areas with strong currents.
Filter feeds (mostly
diatoms) using long setae on its second and third maxillipeds,
and also uses the setal tufts (picture)
to sweep up material from rock surfaces. Crabs of
sometimes live together in groups of males, females, and young; with
dominant males doing most of the breeding. Females often have
broods per year. Has little resistance to
larvae have extremely long, distinctive rostrums.
As with most porcelain crabs, this species will very readily autotomize
if handled. Unlike P. cinctipes,
claw of this species can continue pinching.
and Carlton, 1975
and Brusca, 1978
and Snook, 1955
et al., 1980
and O'Clair, 1998
Russell, Robert M., Jr., 1961. Laboratory culture
stages of Petrolisthes eriomerus Stimpson. Master's thesis,
Walla College. 35 pp.
General Notes and
Observations: Locations, abundances,
This species is moderately common in the lower intertidal of
Porcelain crabs, unlike true crabs, have uropods
on their abdomens.
The undersized fifth leg is visible on porcelain crabs.
The tufts of setae present on the chelipeds
can be seen when the animal is
underwater. Notice also
the blue on the chelipeds.
Photo by Dave Cowles, June 2005
|This individual, found at Swirl
Rocks, clearly shows the
blue coloration present on the maxillipeds
and the chelae.
Photos by Dave Cowles, July 2007
Authors and Editors of Page:
Dave Cowles (2005): Created original page