Dreissena polymorpha sur spongilla lacustris 2014 10 02

Pseudofeces or pseudofaeces are a specialized method of expulsion that filter-feeding

bivalve Bivalvia () or bivalves, in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class (biology), class of aquatic animal, aquatic molluscs (marine and freshwater) that have laterally compressed soft bodies enclosed b ...

mollusk Mollusca is a phylum of protostomic invertebrate animals, whose members are known as molluscs or mollusks (). Around 76,000 extant species of molluscs are recognized, making it the second-largest animal phylum after Arthropoda. The ...

s (and filter-feeding

gastropod Gastropods (), commonly known as slugs and snails, belong to a large Taxonomy (biology), taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, freshwater, and fro ...

mollusks) use in order to get rid of suspended particles such as particles of grit which cannot be used as food, and which have been rejected by the animal. The rejected particles are wrapped in

mucus Mucus (, ) is a slippery aqueous secretion produced by, and covering, mucous membranes. It is typically produced from cells found in mucous glands, although it may also originate from mixed glands, which contain both Serous fluid, serous and muc ...

, and are then expelled without having passed through the

digestive tract The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the Digestion, digestive system that leads from the mouth to the anus. The tract is the largest of the body's systems, after the cardiovascula ...

.Shimek, Ronald L
''Phytoplankton, A Necessity For Clams''
/ref> Thus, although they may closely resemble the mollusk's real feces, they are not actually feces, hence the name pseudofeces, meaning false feces.

Occurrence

Bivalves which exhibit this behavior are numerous and include

Ostreidae The Ostreidae, the true oysters, include most species of molluscs commonly consumed as oysters. Pearl oysters are not true oysters, and belong to the order Pteriida. Like scallops, true oysters have a central adductor muscle, which means the s ...

oyster Oyster is the common name for a number of different families of salt-water bivalve molluscs that live in marine or brackish habitats. In some species, the valves are highly calcified, and many are somewhat irregular in shape. Many, but no ...

s (such as '' Crassostrea'') and Dreissenidae false

mussel Mussel () is the common name used for members of several families of bivalve molluscs, from saltwater and Freshwater bivalve, freshwater habitats. These groups have in common a shell whose outline is elongated and asymmetrical compared with other ...

s (such as '' Dreissena''). Gastropods which filter feed are in a minority, but include the mudsnail genus Batillaria

and deep sea

vent Vent or vents may refer to: Science and technology Biology *Vent, the cloaca region of an animal *Vent DNA polymerase, a thermostable DNA polymerase Geology *Hydrothermal vent, a fissure in a planet's surface from which geothermally heated water ...

limpets in the family Lepetodrilidaebr>

Process

Bivalves have two Siphon (mollusc), siphons or apertures at the ''posterior'' edge of their

mantle cavity The mantle (also known by the Latin word pallium meaning mantle, robe or cloak, adjective pallial) is a significant part of the anatomy of molluscs: it is the dorsal body wall which covers the visceral mass and usually protrudes in the form of ...

: an inhalant or incurrent siphon, and an exhalant or excurrent siphon or aperture. The water is circulated by the action of the

gill A gill () is a respiration organ, respiratory organ that many aquatic ecosystem, aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow r ...

s. Usually water enters the mantle cavity through the inhalant siphon, moves over the gills, and leaves through the exhalent siphon. The water current is utilized for respiration, but it is also used for feeding, and for reproduction. The mouth of the bivalve is situated ''anterior'' to the gills. The bivalve utilizes

phytoplankton Phytoplankton () are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater Aquatic ecosystem, ecosystems. The name comes from the Greek language, Greek words (), meaning 'plant', and (), mea ...

as its food source, but the water circulating through the bivalve also usually contains other particles, such as small grains of sand,

detritus In biology, detritus ( or ) is organic matter made up of the decomposition, decomposing remains of organisms and plants, and also of feces. Detritus usually hosts communities of microorganisms that colonize and decomposition, decompose (Reminera ...

, etc. After moving over the gill margins, particles reach the mouth of the bivalve. Each side of the mouth of the bivalve has an inner and an outer appendage called a palp. The outer palp has a long extensible

proboscis A proboscis () is an elongated appendage from the head of an animal, either a vertebrate or an invertebrate. In invertebrates, the term usually refers to tubular arthropod mouthparts, mouthparts used for feeding and sucking. In vertebrates, a pr ...

, which collects incoming

particulate matter Particulate matter (PM) or particulates are microscopic particles of solid or liquid matter suspended in the air. An ''aerosol'' is a mixture of particulates and air, as opposed to the particulate matter alone, though it is sometimes defin ...

. The particles are then sorted by both the inner and outer palps, which have

ciliate The ciliates are a group of alveolates characterized by the presence of hair-like organelles called cilia, which are identical in structure to flagellum, eukaryotic flagella, but are in general shorter and present in much larger numbers, with a ...

d 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

, to the mouth, using ciliary currents. Some material is rejected because it is too large or too dense: this is often pieces of sediment or detritus, but also includes some overly large edible particles. The outer palps send this rejected material into the mantle cavity as a mucus-bound mass. These mucus-bound masses are the pseudofeces. 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.

Plankton Plankton are the diverse collection of organisms that drift in Hydrosphere, water (or atmosphere, air) but are unable to actively propel themselves against ocean current, currents (or wind). The individual organisms constituting plankton are ca ...

ic 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.

Human relevance

Land runoff Surface runoff (also known as overland flow or terrestrial runoff) is the unconfined flow of water over the ground surface, in contrast to '' channel runoff'' (or ''stream flow''). It occurs when excess rainwater, stormwater, meltwater, or other ...

containing

particulate Particulate matter (PM) or particulates are microscopic particles of solid or liquid matter suspended in the air. An ''aerosol'' is a mixture of particulates and air, as opposed to the particulate matter alone, though it is sometimes define ...

pollutants and excess nutrients often causes problems in

estuaries An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environm ...

and coastal waters. Bivalves can filter the particulate pollutants, and either eat them or discharge them as pseudofeces deposits onto the

benthic The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from the Ancient Greek word (), meaning "the depths". ...

substrate, where they are then relatively harmless.

Chesapeake Bay The Chesapeake Bay ( ) is the largest estuary in the United States. The bay is located in the Mid-Atlantic (United States), Mid-Atlantic region and is primarily separated from the Atlantic Ocean by the Delmarva Peninsula, including parts of the Ea ...

's once-flourishing oyster populations historically filtered the estuary's entire water volume of excess nutrients every three or four days.

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
''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. * Beninger, Peter G; Veniot, Anne and Poussart, Yves (1999
''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
''Ecosystem influences of natural and cultivated populations of suspension-feeding bivalve molluscs: a review''
Journal of Shellfish Research, 1 April 2004.

External links

Flash animation
{{Gastropod anatomy Bivalve anatomy Gastropod anatomy