A rhinophore is one of a pair of

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 ...

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 t ...

, marine

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 ...

opisthobranch Opisthobranchs () is a now 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. Euopistho ...

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 such as the

nudibranchs Nudibranchs () are a group of soft-bodied marine gastropod molluscs, belonging to the order Nudibranchia, that shed their shells after their larval stage. They are noted for their often extraordinary colours and striking forms, and they have be ...

, sea hares (

Aplysiomorpha The order Aplysiida, 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 ...

), and sap-sucking sea slugs (

Sacoglossa Sacoglossa are a superorder of small sea slugs and sea snails, marine gastropod mollusks that belong to the clade Heterobranchia known as sacoglossans. There are 284 valid species recognized within this superorder. Sacoglossans live by ingestin ...

Etymology

The name relates to the rhinophore's function as an organ of "smell". ''Rhino-'' means

nose A nose is a sensory organ and respiratory structure in vertebrates. It consists of a nasal cavity inside the head, and an external nose on the face. The external nose houses the nostrils, or nares, a pair of tubes providing airflow through the ...

from

Ancient Greek Ancient Greek (, ; ) includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Greek ...

ῥίς ''rhis'' and from its genitive ῥινός ''rhinos''. "Phore" means "to bear" from

Neo-Latin Neo-LatinSidwell, Keith ''Classical Latin-Medieval Latin-Neo Latin'' in ; others, throughout. (also known as New Latin and Modern Latin) is the style of written Latin used in original literary, scholarly, and scientific works, first in Italy d ...

''-phorus'' and from Greek -phoros (φορος) "bearing", a derivative of ''phérein'' (φέρειν).

Function

Rhinophores are

scent An odor (American English) or odour (English in the Commonwealth of Nations, Commonwealth English; American and British English spelling differences#-our, -or, see spelling differences) is a smell or a scent caused by one or more volatilized ...

taste The gustatory system or sense of taste is the sensory system that is partially responsible for the perception of taste. Taste is the perception stimulated when a substance in the mouth biochemistry, reacts chemically with taste receptor cells l ...

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 or sea sponges are primarily marine invertebrates of the animal phylum Porifera (; meaning 'pore bearer'), a basal clade and a sister taxon of the diploblasts. They are sessile filter feeders that are bound to the seabed, and ar ...

) 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 ser ...

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 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 ...

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 receptor potentials. This process is called sensory transduc ...

s that project

axon An axon (from Greek ἄξων ''áxōn'', axis) or nerve fiber (or nerve fibre: see American and British English spelling differences#-re, -er, spelling differences) is a long, slender cellular extensions, projection of a nerve cell, or neuron, ...

s back to rhinophore

ganglia A ganglion (: ganglia) 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 a ...

and

dendrite A dendrite (from Ancient Greek language, Greek δένδρον ''déndron'', "tree") or dendron is a branched cytoplasmic process that extends from a nerve cell that propagates the neurotransmission, electrochemical stimulation received from oth ...

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 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 rights ...