Pinnixa faba

From ize

Known as a pea crab, Pinnixa faba (Dana, 1851) is a symbiont of Tresus capax in its mature stage.

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

Contents 1 Description 2 Life History 3 Diet 4 Misidentification 5 Range 6 Footnotes

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 ^[1]

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. ^[2]

Life History

P. faba are only known to mate in 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 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 Saxidomus giganteus ^[3]

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. ^[4]

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 ^[5]

Footnotes

1. ↑ 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
2. ↑ 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.
3. ↑ 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.
4. ↑ 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.
5. ↑ 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