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[[Image:Underside_of_crab_et.jpg|thumb|Ventral view of ''Pinnixa faba'']] [[Image:Crab folded up et.jpg|thumb|Dorsal view of ''Pinnixa faba'']] [[Image:Crab attack.jpg|thumb|Anterior view of ''Pinnixa faba'']] 
Known as a pea crab, ''Pinnixa faba'' (Dana, 1851) is a symbiont of [http://biota.evergreen.edu/animalia/mollusca/bivalvia/veneroida/mactridae/tresus/tresus-capax/ ''Tresus capax''] in its mature stage.  

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! Taxonomy
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| Kingdom: Animalia
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| Phylum: Arthropoda
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| Subphylum: Crustacea
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| Class: Malacostraca
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| Superorder: Eucarida
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| Order: Decapoda
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| Suborder: Pleocyemata
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| Infraorder: Brachyura
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| Section: Brachyrhyncha
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| Family: Pinnotheridae
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| Genus: ''Pinnixa''
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| Species: ''P. faba''
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==Description==

Pea Crabs, Family Pinnotheridae, are small crabs that live symbiotically with clams, tubeworms, sea cucumbers, and other fauna.  Usually feeding of of the results of their host's filtering, or in the case of sea cucumbers they live in the cloaca feeding off of the results of digestion and reproduction.  They have no rostrum and no teeth between the eyes <ref>Cowles, D. (2005). ''Pinnixa faba''. Retrieved May 20, 2008, from Walla Walla University, Rosario Beach Web site, http://www.wallawalla.edu/academics/departments/biology/rosario/inverts/Arthropoda/Crustacea/Malacostraca/Eumalacostraca/Eucarida/Decapoda/Brachyura/Family_Pinnotheridae/Pinnixa_faba.html#face</ref>

The carapace gets up to 15 mm wide and 7 mm long.  The carapace and walking legs are often covered in setae which can collect the material being filtered by the host.  The species is distinguished by the tips of the dactyls which are are noticeably curved and rounded nature of the outer eye orbits. <ref>Zmarzly, D. L. (1992). Taxonomic review of pea crabs in the genus Pinnixa (Decapoda: Brachyura: Pinnotheridae) Occurring on the California Shelf, with descriptions of two new species. ''Journal of Crustacean Biology, 12(4),'' 677-713. </ref>

==Life History==

''P. faba'' are only known to mate in [http://biota.evergreen.edu/animalia/mollusca/bivalvia/veneroida/mactridae/tresus/tresus-capax/ ''Tresus capax''] where somehow juveniles are prevented from maturing until one member of the breeding couple dies or the juvenile finds another host.  In a breeding couple the female will remain in the visceral fold feeding off of the materiel filtered by [http://biota.evergreen.edu/animalia/mollusca/bivalvia/veneroida/mactridae/tresus/tresus-capax/ ''Tresus capax''] while the male and juveniles roam around the mantle cavity.  Juveniles can be found in most other clams found on The Evergreen Beach, notably [http://biota.evergreen.edu/animalia/mollusca/bivalvia/veneroida/veneridae/saxidomus/saxidomus-giganteus/''Saxidomus giganteus''] <ref>Zmarzly, D. L. (1992). Taxonomic review of pea crabs in the genus Pinnixa (Decapoda: Brachyura: Pinnotheridae) Occurring on the California Shelf, with descriptions of two new species. ''Journal of Crustacean Biology, 12(4),'' 677-713. </ref>

Some writers consider the relationship of ''P. faba'' with it's hosts to be commensalistic while others consider it parasitic, though it is clear that ''P. faba'''s symbiosis causes minimal if any damage to the host

==Diet==

''P. faba'' feeds on the filtered organic matter collected by its host

==Misidentification==

''P. faba'' is indistinguishable from ''P. littoralis'' without magnification.  ''P. littoralis'' has a more angular shape to the outer eye orbit while ''P. faba'' does not leave a significant gap when it closes it's chelapeds. <ref>Zmarzly, D. L. (1992). Taxonomic review of pea crabs in the genus Pinnixa (Decapoda: Brachyura: Pinnotheridae) Occurring on the California Shelf, with descriptions of two new species. ''Journal of Crustacean Biology, 12(4),'' 677-713. </ref>

==Range==

P. faba is found among its hosts in the intertidal regions of Prince of Wales Island, Alaska to Newport Beach, CA., most common in Puget Sound <ref>Cowles, D. (2005). ''Pinnixa faba''. Retrieved May 20, 2008, from Walla Walla University, Rosario Beach Web site, http://www.wallawalla.edu/academics/departments/biology/rosario/inverts/Arthropoda/Crustacea/Malacostraca/Eumalacostraca/Eucarida/Decapoda/Brachyura/Family_Pinnotheridae/Pinnixa_faba.html#face</ref>


==Footnotes==
<references/>