Sensory organs of gastropods (snails and slugs) include olfactory organs, eyes, statocysts and mechanoreceptors.^[1] Gastropods have no sense of hearing.^[1]

[edit] Olfactory organs

Rhinophores of Aplysia californica.

The upper pair of tentacles on the head of the edible snail Helix pomatia have eyes, but the main sensory organs are sensory neurons for olfaction in the epithelium of the tentacles.

In terrestrial gastropods the most important sensory organs are the olfactory organs which are located on the tips of the 4 tentacles.^[1]

In opisthobranch marine gastropods, the chemosensory organs are two protruding structures on top of the head. These are known as rhinophores.

An opisthobranch Navanax inermis has chemoreceptors at sides of its mouth in and it can to track mucopolysaccharides from the slime trails of prey, and of potential mates.^[2]

Freshwater snail Bithynia tentaculata is capable of detecting the presence of molluscivorous leeches through chemoreception and of closing its operculum to avoid predation.^[3]

[edit] Eyes

Well-developed lens eye of Eustrombus gigas on eyestalk has a black iris. There is a small tentacle on the eyestalk also.

In terrestrial pulmonate gastropods eye spots are present at the tip of the tentacles in the Stylommatophora or at the base of the tentacles in the Bassommatophora. These eye spots range from simple ocelli that cannot project an image (simply distinguishing light and dark), to more complex pit and even lens eyes.^[4] Vision is not the most important requirement in terrestrial gastropods, because they are mainly nocturnal animals.^[1]

Some gastropods, for example the freshwater Apple snails (family Ampullariidae)^[5] and marine species of genus Strombus^[6] can completely regenerate their eyes. The gastropods in both of these families have lens eyes.

[edit] Ocelli

Ocelli

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[edit] Pit eyes

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[edit] Lens eyes

Drawing of cross section of the eye of Helix pomatia.
1 - lens
2 - olfactory epithelium
3 - corneal epithelium
4 - corneal endothelium
5 - retina
6 - layer with rod cells
7 - fibrous connective tissue layer
8 - nerve of the eye

Drawing of cross sections of the extracted tentacle (left) and constricted tentacle (right) with and eye of Helix pomatia.
1 - nerve of an eye
2 -
3 -
4 - eye
5 - tentacle ganglion
6 - epidermis
7 -
8 - nerve of an tentacle
9 - retractor muscle
10 -

another drawing of eye of Helix pomatia

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[edit] Statocysts

In the statocysts of Haliotis asinina was found the expression of a conserved gene (Pax-258 gene), which is also important for forming structures for balance in eumetazoans.^[7]

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[edit] Mechanoreceptors

Mechanoreceptor

This section requires expansion.

[edit] References

[edit] Further reading

• Sergei Tschachotin. 1908. Die Statocyste der Heteropoden. Heidelberg, Univ., Diss., (Zeitschrift f. wissenschaftl. Zoologie; Bd. 90; S. 343-422).
• Abraham J. Susswein, Mitchell S. Cappell & Michael V. L. Bennett 1982. Distance chemoreception in Navanax inermis. Marine and Freshwater Behaviour and Physiology, Volume 8, Issue 3 April 1982, pages 231-241.

[edit] External links