Porcelain Crab

(also called Flattop Crab)


Petrolisthes eriomerus


Class Malacostraca,

Order Decapoda,

Infraorder Anomura

Family Porcellanidae



Eastern Pacific, ranging from Chichagof, Alaska, south to La Jolla, California.[1] 


Range from the lower intertidal to depth around 80 meters.  Usually prefer to live in areas of high wave action2 under rocks that rest on sand or fine gravel,[2] or in kelp holdfasts or mussel beds.1


Porcelain crabs tend to live together in groups of males, females, and juveniles.  Within these groups, several dominant males are responsible for most of the breeding.1  Females usually have 2 broods per year.1


Have pelagic zoeal larvae with large, inflexible rostral spines[3] that are important for protection against predation.  In its larval stage, it uses its first two maxillipeds to swim.3 The larvae then develop into a megalopa form (glaucathoe).  Once megalopae come in contact with adults, they lose the ability to swim and begin acting like juveniles.  However, they do not molt until a week or more later.[4] Juveniles have been found to associate closely with adults (even without kinship), sometimes hiding underneath them for protection.4



Mainly filter feed using long setae, mainly feeding on diatoms.  Also, sweep up food from rock surfaces using setal tufts on claws.1


The porcelain crab is an Anomuran, however, unlike other Anomuran crabs, the undersized 5th pair of appendages can clearly be seen in porcelain crabs.1  If threatened or disturbed, the porcelain crab can drop one of its appendages, which will eventually grow back2  and unlike the similar species, P. cinctipes, the dropped claw can continue to pinch.1  Some members of the genus Porcellanidae  have a unique decalcified area (“leg membranes”) on their walking legs that act as respiratory structures during times of increased metabolic demands.[5]


No known commercial value.


[1] Cowles, Dave. Petrolisthes eriomerus Stimpson, 1871. 2005. http://www.rosario.wwc.edu/inverts/Arthropoda/Crustacea/Malacostraca/Eumalacostraca/Eucarida/Decapoda/Anomura/Family_Porcellanidae/Petrolisthes_eriomerus.html; 7 May 2007.


[2] Adams, Mary Jo.  Petrolisthes eriomerus (Porcelain crab).  December 5, 2005.  http://www.beachwatchers.wsu.edu/ezidweb/animals/Petrolisthes.htm; 23 April 2007.


[3] Marine Invertebrate Zoology Class. Invertebrates in the Plankton: Arthropoda. Friday Harbor, 2000.   http://depts.washington.edu/fhl/zoo432/plankton/plarthropoda/plarthropoda.html; 23 April 2007.


[4] Jensen, Greg C.  Competition, settlement behavior, and post-settlement aggregation by the Porcelain crab.  Journal of Exp Marine Biology and Ecology.  153(1): 49-61.


[5] Stillman, Jonathan H.  Evolutionary History and Adaptive Significance of Respiratory Structures on the Legs of Intertidal Porcelain Crabs, Genus Petrolisthe, Physiological and Biochemical Zoology 73(1):86–96. 2000.