The osphradium is a pigmented

chemosensory A chemoreceptor, also known as chemosensor, is a specialized sensory receptor which transduces a chemical substance (endogenous or induced) to generate a biological signal. This signal may be in the form of an action potential, if the chemorecept ...

epithelium Epithelium or epithelial tissue is a thin, continuous, protective layer of cells with little extracellular matrix. An example is the epidermis, the outermost layer of the skin. Epithelial ( mesothelial) tissues line the outer surfaces of man ...

patch in the mantle cavity present in six of the eight extant

class Class, Classes, or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytical concept used d ...

es of

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

(it is absent in the

Scaphopoda Scaphopoda (plural scaphopods , from Ancient Greek σκᾰ́φης ''skáphē'' "boat" and πούς ''poús'' "foot"), whose members are also known as tusk shells or tooth shells, are a class of shelled marine invertebrates belonging to the ph ...

and

Monoplacophora Shell of Monoplacophora Monoplacophora , meaning "bearing one plate", is a polyphyletic class of molluscs with a cap-like shell, inhabiting deep sea environments. Extant representatives were not recognized as such until 1952; previously they wer ...

; most

Cephalopoda A cephalopod is any member of the molluscan class Cephalopoda ( Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, ...

also lack it, but the

nautilus A nautilus (; ) is any of the various species within the cephalopod family Nautilidae. This is the sole extant family of the superfamily Nautilaceae and the suborder Nautilina. It comprises nine living species in two genera, the type genus, ty ...

has what appears to be a set of osphradia ), on or adjacent to the ctenidia (gills). The main function of this organ is disputed but it is believed to be used to test incoming water for

silt Silt is granular material of a size between sand and clay and composed mostly of broken grains of quartz. Silt may occur as a soil (often mixed with sand or clay) or as sediment mixed in suspension (chemistry), suspension with water. Silt usually ...

and possible food particles or, in some species, for sensing the presence of light. It is a popular idea among

malacologist Malacology, from Ancient Greek μαλακός (''malakós''), meaning "soft", and λόγος (''lógos''), meaning "study", is the branch of invertebrate zoology that deals with the study of the Mollusca (molluscs or mollusks), the second-largest ...

s that the presence of an osphradium should be a molluscan

synapomorphy In phylogenetics, an apomorphy (or derived trait) is a novel Phenotypic trait, character or character state that has evolution, evolved from its ancestral form (or Plesiomorphy and symplesiomorphy, plesiomorphy). A synapomorphy is an apomorphy sh ...

. However, an osphradium is absent in monoplacophorans and scaphopods. Moreover, the differences in enervation of these patches suggest that the osphradium (as a patch enervated from the ctenidial nerve) may be different from another organ sometimes called the posterior sensory organ (PSO) with separate enervation from the lateral nerve cords. Both types of sensory organs are found in the nautilus.

References

External links

* Hulbert G. C. E. B. & Yonge C. M. (1937). "A Possible Function of the Osphradium in the Gastropoda". ''

Nature Nature is an inherent character or constitution, particularly of the Ecosphere (planetary), ecosphere or the universe as a whole. In this general sense nature refers to the Scientific law, laws, elements and phenomenon, phenomena of the physic ...

'' 139: 840-841. . * Brown A. C. & Noble R. G. (1960). "Function of the Osphradium in ''Bullia'' (Gastropoda)". ''

'' 188: 1045-1045. . Cephalopod zootomy Gastropod anatomy {{Gastropod-stub