Rhinophore

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A pair of rhinophores on the head of Chromodoris coi Chromodoris coi rhinophores.jpg
A pair of rhinophores on the head of Chromodoris coi
Right rhinophore of Acanthodoris pilosa Acanthodoris pilosa rhinophore.jpg
Right rhinophore of Acanthodoris pilosa

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 gastropod opisthobranch mollusks such as the nudibranchs, sea hares (Aplysiomorpha), and sap-sucking sea slugs (Sacoglossa).

Contents

Etymology

The name relates to the rhinophore's function as an organ of "smell". Rhino- means nose from Ancient Greek 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 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). [1]

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. [2] This allows the nudibranchs to stay close to their food source (for example species of sponges) and to find mates. In the sea hare Aplysia californica , the rhinophores are able to detect pheromones. [1]

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. [2]

Structure

Rhinophores of Aplysia californica Aplysia californica rhinophore.jpg
Rhinophores of Aplysia californica

In reproductively mature Aplysia adults, the rhinophore is about 1 cm in length. [1] The neuroanatomical organization includes a rhinophore groove where most of the sensory cells appear to be concentrated. Its sensory epithelium contains sensory neurons that project axons back to rhinophore ganglia and dendrites that end in either a surface-exposed cilium or a small protuberance. [1]

A low-power scanning electron microscopy (SEM) micrograph showing the rhinophore tip of Aplysia californica
Scale bar is 300 mm.
rg - rhinophore groove
tip - rhinophore tip. Aplysia californica rhinophore 2.jpg
A low-power scanning electron microscopy (SEM) micrograph showing the rhinophore tip of Aplysia californica
Scale bar is 300 μm.
rg - rhinophore groove
tip - rhinophore tip.
A medium-power SEM image showing the cilia-bearing epithelium within the rhinophore groove
Scale bar is 100 mm.
f - folds Aplysia californica rhinophore 3.jpg
A medium-power SEM image showing the cilia-bearing epithelium within the rhinophore groove
Scale bar is 100 μm.
f - folds
A high-power SEM image showing cilia extending from a common pore: Also evident are pores lacking obvious bunched cilia.
Scale bar is 10 mm.
ci - numerous long cilia Aplysia californica rhinophore 4.jpg
A high-power SEM image showing cilia extending from a common pore: Also evident are pores lacking obvious bunched cilia.
Scale bar is 10 μm.
ci - numerous long cilia

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. [1]

Related Research Articles

Nudibranch Order of gastropods

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, such as "clown", "marigold", "splendid", "dancer", "dragon", or "sea rabbit". Currently, about 3,000 valid species of nudibranchs are known.

A chemoreceptor, also known as chemosensor, is a specialized sensory receptor which transduces a chemical substance to generate a biological signal. This signal may be in the form of an action potential, if the chemoreceptor is a neuron, or in the form of a neurotransmitter that can activate a nerve fiber if the chemoreceptor is a specialized cell, such as taste receptors, or an internal peripheral chemoreceptor, such as the carotid bodies. In physiology, a chemoreceptor detects changes in the normal environment, such as an increase in blood levels of carbon dioxide (hypercapnia) or a decrease in blood levels of oxygen (hypoxia), and transmits that information to the central nervous system which engages body responses to restore homeostasis.

California sea hare Species of gastropod

The California sea hare is a species of sea slug in the sea hare family, Aplysiidae. It is found in the Pacific Ocean, off the coast of California in the United States and northwestern Mexico.

Anaspidea Clade of gastropods

The clade Anaspidea, commonly known as sea hares, are medium-sized to very large opisthobranch gastropod molluscs with a soft internal shell made of protein. These are marine gastropod molluscs in the superfamilies Aplysioidea and Akeroidea.

Sea slug Group of marine invertebrates with varying levels of resemblance to terrestrial 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 that over evolutionary time have either completely lost their shells, or have seemingly lost their shells due to having a greatly reduced or internal shell. The name "sea slug" is most often applied to nudibranchs, as well as to a paraphyletic set of other marine gastropods without obvious shells.

Opisthobranchia Informal group of gastropods

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.

Aplysiidae Family of gastropods

Aplysiidae is the only family in the superfamily Aplysioidea, within the clade Anaspidea. These animals are commonly called sea hares because, unlike most sea slugs, they are often quite large, and when they are underwater, their rounded body shape and the long rhinophores on their heads mean that their overall shape resembles that of a sitting rabbit or hare. Sea hares are however sea snails with shells reduced to a small plate hidden between the parapodia, and some species are extremely large. The Californian black sea hare, Aplysia vaccaria is arguably the largest living gastropod species, and is certainly the largest living heterobranch gastropod.

Cephalaspidea Order of gastropods

The order Cephalaspidea, also known as the headshield slugs and bubble snails, is a major taxon of sea slugs and bubble snails, marine gastropod mollusks within the larger clade Euopisthobranchia. Bubble shells is another common name for these families of marine gastropods, some of which have thin bubble-like shells. This clade contains more than 600 species.

<i>Flabellinopsis iodinea</i> Species of gastropod

Flabellinopsis iodinea, the Spanish shawl, is a species of aeolid nudibranch, a very colorful sea slug. This is a marine gastropod mollusk in the family Flabellinidae.

<i>Elysia pusilla</i> Species of gastropod

Elysia pusilla is a species of small sea slug, a marine gastropod mollusk in the family Plakobranchidae. It is a sacoglossan.

<i>Aplysia punctata</i> Species of gastropod

Aplysia punctata is a species of sea slug in the family Aplysiidae, the sea hares. It reaches a length of up to 20 cm (7.9 in) and is found in the northeast Atlantic, ranging from Greenland and Norway to the Mediterranean Sea.

<i>Chromodoris westraliensis</i> Species of gastropod

Chromodoris westraliensis is a species of very colourful sea slug, a dorid nudibranch, a marine gastropod mollusc in the family Chromodorididae.

The sensory organs of gastropods include olfactory organs, eyes, statocysts and mechanoreceptors. Gastropods have no sense of hearing.

<i>Aplysia vaccaria</i> Species of gastropod

Aplysia vaccaria, also known as the black sea hare and California black sea hare, is a species of extremely large sea slug, a marine, opisthobranch, gastropod mollusk in the family Aplysiidae. It is the largest sea slug species.

<i>Chromodoris orientalis</i> Species of gastropod

Chromodoris orientalis is a species of colourful sea slug, a dorid nudibranch, a marine gastropod mollusc in the family Chromodorididae. Sea slugs are generally very beautifully colored organisms with intense patterns and ranging in sizes. The Chromodoris orientalis specifically is a white sea slug with black spots in no particular pattern with a yellow, orange, or brown in color ring around its whole body and on its gills. There is much discussion on where it is found, what it eats, how it defends itself without a shell, and its reproduction methods. This is all sought after information because there is not much known about these animals.

<i>Berghia stephanieae</i> Species of gastropod

Berghia stephanieae is a species of sea slug, an aeolid nudibranch. It is a marine gastropod mollusc in the family Aeolidiidae. It was previously known as Aeolidiella stephanieae.

Phagomimicry

Phagomimicry is a defensive behaviour of sea hares, in which the animal ejects a mixture of chemicals, which mimic food, and overwhelm the senses of their predator, giving the sea hare a chance to escape. The typical defence response of the sea hare to a predator is to release two chemicals - ink from the ink gland and opaline from the opaline gland. While ink creates a dark, diffuse cloud in the water which disrupts the sensory perception of the predator by acting as a smokescreen and as a decoy, the opaline, which affects the senses dealing with feeding, causes the predator to instinctively attack the cloud of chemicals as if it were indeed food. This ink is able to mimic food by having a high concentration of amino acids and other compounds that are normally found in food, and the attack behaviour of the predator allows the sea-hares the opportunity to escape.

<i>Aeolidiella alderi</i> Species of gastropod

Aeolidiella alderi is a species of sea slug, an aeolid nudibranch in the family Aeolidiidae. It is native to northwestern Europe where it occurs in the intertidal zone. It is a predator and feeds on sea anemones.

Aplysia morio, the Atlantic black sea hare or sooty sea hare, is a species of sea slug, a marine gastropod mollusk in the family Aplysiidae, the sea hares. It lives in warm waters in the Caribbean Sea and off the south and southeastern coast of the United States, where it feeds on seaweed.

<i>Aplysia gigantea</i> Species of mollusc in the family Aplysiidae

Aplysia gigantea is a species of sea slug, a shell-less marine gastropod mollusk in the family Aplysiidae. The species was first described in the Journal of the Malacological Society of Australia in 1869. A. gigantea is also known more commonly as the sea hare due to their posterior chemosensory tentacles resembling a hare's ear. A. gigantea is the largest known species in Australia of the opisthobranch genus. The species is known to have toxic effects on terrestrial organisms, particularly domestic dogs. Exposure to this species with dogs has been associated with the development of neurotoxicosis, with symptoms ranging from respiratory distress to tremors, muscle fasciculations, and seizures.

References

This article incorporates CC-BY-2.0 text (but not under GFDL) from reference. [1]

  1. 1 2 3 4 5 6 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 2009, 7:28. doi : 10.1186/1741-7007-7-28.
  2. 1 2 Rhinophore in nudibranchs Archived 2007-10-21 at the Wayback Machine . Sea Slug Forum, accessed 8 July 2009.

Further reading