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 Sea slug is a common name for some marine invertebrates with varying levels of resemblance to terrestrial slugs. Most creatures known as sea slugs are gastropods, i.e. they are sea snails (marine gastropod mollusks) that over evolutionary tim ...

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. Euopisth ...

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 Nudibranchs () are a group of soft-bodied marine gastropod molluscs which shed their shells after their larval stage. They are noted for their often extraordinary colours and striking forms, and they have been given colourful nicknames to match, ...

, sea hares (

Aplysiomorpha The clade Anaspidea, commonly known as sea hares (''Aplysia'' species and related genera), are medium-sized to very large opisthobranch gastropod molluscs with a soft internal shell made of protein. These are marine gastropod molluscs in the s ...

), 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 passes th ...

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 peri ...

ῥίς ''rhis'' and from its genitive ῥινός ''rhinos''. "Phore" means "to bear" from New Latin ''-phorus'' and from Greek -phoros (φορος) "bearing", a derivative of ''phérein'' (φέρειν).

Function

Rhinophores are scent 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 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 ...

) 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 pheromones.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 cell ...

s that project axons 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 sympatheti ...

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 n ...

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

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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 the r ...