Pseudofeces

Pseudofeces or pseudofaeces are a specialized method of expulsion that filter-feeding bivalve mollusks (and filter-feeding gastropod 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, and are then expelled without having passed through the digestive tract. Thus, although they may closely resemble the mollusk's real feces, they are not actually feces, hence the name pseudofeces, meaning false feces.

Bivalves which exhibit this behavior are numerous and include Ostreidae oysters (such as Crassostrea) and Dreissenidae false mussels (such as Dreissena). Gastropods which filter feed are in a minority, but include the mudsnail genus Batillaria[1] and deep sea vent limpets in the family Lepetodrilidae.[2]

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. The water is circulated by the action of the gills. Usually water enters the mantle cavity through the inhalent 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 as its food source, but the water circulating through the bivalve also usually contains other particles, such as small grains of sand, detritus, etc.

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