Pseudofeces

Pseudofeces, (or pseudofaeces — see spelling differences) are a way filter-feeding bivalve mollusks get rid of suspended particles which have been rejected as unsuitable for food. Mollusks which exhibit this behaviour include oysters (such as "Crassostrea") and mussels (such as "Dreissena"). The rejected particles are wrapped in mucus, and are expelled without having passed through the digestive tract.Shimek, Ronald L. [http://www.dtplankton.com/articles/necessity.html "Phytoplankton, A Necessity For Clams"] ]

Bivalves have two siphons or apertures at the posterior edge of their mantle cavity: an inhalant or incurrent siphon, and an exhalant or excurrent siphon or aperture. Usually water is brought into the mantle cavity through the inhalant siphon, moves over the gills, and leaves through the exhalant siphon. The water current is utilized for respiration, feeding, and reproduction.

After moving over the gill margins, particles reach the mouth of the bivalve. Each side of the mouth has an inner and an outer appendage called a palp. The outer palp has a long extensible proboscis, which collects incoming particulate matter. The particles are then sorted by both the inner and outer palps, which have ciliated grooves for collecting organic material. These food grooves sort the particles by both density and size. The inner pair of palps transfers smaller and lighter particles, such as phytoplankton, to the mouth, using ciliary currents. The outer palps send the rejected material, often particles of sediment, which are heavy or larger, into the mantle cavity as a mucus-bound mass. This is the pseudofeces. [ [http://www.britannica.com/EBchecked/topic/481273/pseudofeces Pseudofeces] (2008). Retrieved September 23, 2008, from Encyclopædia Britannica Online]

Pseudofeces accumulate with, and look much like, the actual feces in the bottom of the mantle cavity. The unwanted material is periodically ejected (usually through the inhalant siphon or aperture) by contractions of the adductor muscles, which "clap" the shells together, pushing most of the water out of the mantle cavity and forcibly ejecting both the feces and the pseudofeces.

Planktonic food is not usually in short supply, and therefore accidentally rejecting a few larger edible particles along with the larger or denser inedible ones is a small price to pay in order to optimize the processing of the rest of the food.

Land runoff containing particulate pollutants and excess nutrients can cause problems in estuaries and coastal waters. Bivalves can filter the particulate pollutants, and either eat them or discharge them as pseudofeces deposits onto the substrate, where they are relatively harmless. Chesapeake Bay's once-flourishing oyster populations historically filtered the estuary's entire water volume of excess nutrients every three or four days. [cite web|url=http://habitat.noaa.gov/restorationtechniques/public/habitat.cfm?HabitatID=2&HabitatTopicID=11|title=Oyster Reefs: Ecological importance|publisher=US National Oceanic and Atmospheric Administration |accessdate=2008-09-24]

Notes

References

* Alexander, Jeffrey A; Stoecker, Diane K; Meritt, Donald W; Alexander, Stephanie T; Padeletti, Angela; Johns, Desmond; Heukelem, Laurie van and Glibert, Patricia M (2008) [http://findarticles.com/p/articles/mi_m0QPU/is_3_27/ai_n26672082/pg_1?tag=artBody;col1 "Differential production of feces and pseudofeces by the oyster Crassostrea ariakensis when exposed to diets containing harmful dinoflagellate and raphidophyte species"] Journal of Shellfisheries Research.
* Beningerll, Peter G; Veniot, Anne and Poussart, Yves (1999) [http://www.int-res.com/articles/meps/178/m178p259.pdf "Principles of pseudofeces rejection on the bivalve mantle: integration in particle processing"] Marine Ecology Progress Series. Vol 178, pp 259–269.
* Newell, Roger I E (2004) [http://www.accessmylibrary.com/coms2/summary_0286-2957037_ITM "Ecosystem influences of natural and cultivated populations of suspension-feeding bivalve molluscs: a review"] Journal of Shellfish Research, 1 April 2004.

External links

* [http://bio.classes.ucsc.edu/bio136/LabManual/Mytilus-Venus/Ven_dig.jpgDrawing of the anatomic structure of a bivalve (showing the palps and other pseudofeces-producing structures). Bio 136: Invetebrate Zoology. Department of Biological Sciences. University of California, Santa Cruz.]
* [http://el.erdc.usace.army.mil/zebra/zmis/zmishelp/impacts_of_pseudofeces_in_the_benthos.htm Impacts of Pseudofeces in the Benthos]
* [http://www.biology.ualberta.ca/courses.hp/zool250/animations/Clam.swf Flash animation]