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A rhinophore is one of a pair of chemosensory club-shaped, rod-shaped or ear-like structures which are the most prominent part of the external head anatomy in sea slugs,
marine Marine is an adjective meaning of or pertaining to the sea or ocean. Marine or marines may refer to: Ocean * Maritime (disambiguation) * Marine art * Marine biology * Marine debris * Marine habitats * Marine life * Marine pollution Military ...
gastropod The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, from freshwater, and from land. T ...
opisthobranch Opisthobranchs () is now an informal name for a large and diverse group of specialized complex gastropods which used to be united in the subclass Opisthobranchia. That taxon is no longer considered to represent a monophyletic grouping. Euopi ...
mollusk Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000  extant species of molluscs are recognized. The number of fossil species is e ...
s such as the nudibranchs, sea hares ( Aplysiomorpha), and sap-sucking sea slugs ( Sacoglossa).


Etymology

The name relates to the rhinophore's function as an organ of "smell". ''Rhino-'' means
nose A nose is a protuberance in vertebrates that houses the nostrils, or nares, which receive and expel air for respiration alongside the mouth. Behind the nose are the olfactory mucosa and the sinuses. Behind the nasal cavity, air next passe ...
from
Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Dark Ages (), the Archaic pe ...
ῥίς ''rhis'' and from its genitive ῥινός ''rhinos''. "Phore" means "to bear" from
New Latin New Latin (also called Neo-Latin or Modern Latin) is the revival of Literary Latin used in original, scholarly, and scientific works since about 1500. Modern scholarly and technical nomenclature, such as in zoological and botanical taxonomy ...
''-phorus'' and from Greek -phoros (φορος) "bearing", a derivative of ''phérein'' (φέρειν).


Function

Rhinophores are
scent An odor (American English) or odour (Commonwealth English; see spelling differences) is caused by one or more volatilized chemical compounds that are generally found in low concentrations that humans and animals can perceive via their sense ...
or
taste The gustatory system or sense of taste is the sensory system that is partially responsible for the perception of taste (flavor). Taste is the perception produced or stimulated when a substance in the mouth reacts chemically with taste receptor ...
receptors, also known as chemosensory organs situated on the dorsal surface of the head. They are primarily used for distance
chemoreception 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 ...
and rheoreception (response to water current). The "scents" detected by rhinophores are chemicals dissolved in the sea water. The fine structure and hairs of the rhinophore provide a large surface area so that chemical detection is maximized. This allows the nudibranchs to stay close to their food source (for example species of
sponges Sponges, the members of the phylum Porifera (; meaning 'pore bearer'), are a basal animal clade as a sister of the diploblasts. They are multicellular organisms that have bodies full of pores and channels allowing water to circulate through t ...
) and to find mates. In the sea hare ''
Aplysia californica The California sea hare (''Aplysia californica'') is a species of sea slug in the sea hare family, Aplysiidae.Rosenberg, G.; Bouchet, P. (2011). Aplysia californica J. G. Cooper, 1863. Accessed through: World Register of Marine Species at http:/ ...
'', the rhinophores are able to detect
pheromone A pheromone () is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting like hormones outside the body of the secreting individual, to affect the behavio ...
s.Scott F Cummins, Dirk Erpenbeck, Zhihua Zou, Charles Claudianos, Leonid L Moroz, Gregg T Nagle & Bernard M Degnan. 2009
''Candidate chemoreceptor subfamilies differentially expressed in the chemosensory organs of the mollusc Aplysia''
BMC Biology ''BMC Biology'' is an online open access scientific journal that publishes original, peer-reviewed research in all fields of biology, together with opinion and comment articles. The publication was established in 2003. The journal is part of a s ...
2009, 7:28. .


Protection

To protect the prominent rhinophores against nibbling by predators, including fish, most species of dorid nudibranchs are able to withdraw their rhinophores into a pocket beneath the skin.''Rhinophore in nudibranchs''
. Sea Slug Forum, accessed 8 July 2009.


Structure

In reproductively mature ''Aplysia'' adults, the rhinophore is about 1 cm in length. The neuroanatomical organization includes a rhinophore groove where most of the sensory cells appear to be concentrated. Its sensory
epithelium Epithelium or epithelial tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. It is a thin, continuous, protective layer of compactly packed cells with a little intercellul ...
contains
sensory neuron Sensory neurons, also known as afferent neurons, are neurons in the nervous system, that convert a specific type of stimulus, via their receptors, into action potentials or graded potentials. This process is called sensory transduction. The ...
s that project
axon An axon (from Greek ἄξων ''áxōn'', axis), or nerve fiber (or nerve fibre: see spelling differences), is a long, slender projection of a nerve cell, or neuron, in vertebrates, that typically conducts electrical impulses known as action p ...
s back to rhinophore
ganglia A ganglion is a group of neuron cell bodies in the peripheral nervous system. In the somatic nervous system this includes dorsal root ganglia and trigeminal ganglia among a few others. In the autonomic nervous system there are both sympathe ...
and
dendrite Dendrites (from Greek δένδρον ''déndron'', "tree"), also dendrons, are branched protoplasmic extensions of a nerve cell that propagate the electrochemical stimulation received from other neural cells to the cell body, or soma, of the ...
s that end in either a surface-exposed cilium or a small protuberance.


Comparison with oral tentacles

In ''A. californica'', the oral tentacles, which are situated in a more ventral position, are possibly involved in contact chemoreception and mechanoreception.


References

This article incorporates CC-BY-2.0 text (but not under
GFDL The GNU Free Documentation License (GNU FDL or simply GFDL) is a copyleft license for free documentation, designed by the Free Software Foundation (FSF) for the GNU Project. It is similar to the GNU General Public License, giving readers th ...
) from reference.


Further reading

* Wertz A., Rössler W., Obermayer M. & Bickmeyer U. (6 April 2006) "Functional neuroanatomy of the rhinophore of ''Aplysia punctata''". '' Frontiers in Zoology'' 3: 6. {{Gastropod anatomy Gastropod anatomy