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Pulmonate land snails usually have two sets of tentacles on their head: the upper pair have an eye at the end; the lower pair are for olfaction. [1]In anatomy, an eyestalk (sometimes spelled eye stalk and also known as an ommatophore) is a protrusion that extends an eye away from the body, giving the eye a better field of view. [1]
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 ...
In terrestrial gastropods (land snails and slugs), the olfactory organs, located on the tips of the four tentacles, are the most important sensory organ. [23] The chemosensory organs of opisthobranch marine gastropods are called rhinophores. The majority of gastropods have simple visual organs, eye spots either at the tip or base of the tentacles.
In most land snails the eyes are carried on the first (upper) set of tentacles (called ommatophores or more informally 'eye stalks') which are usually roughly 75% of the width of the eyes. The second (lower) set of tentacles act as olfactory organs. Both sets of tentacles are retractable in land snails.
Front view of land snail showing upper and lower sets of tentacles Abalone showing pallial tentacles. Many molluscs have tentacles of one form or another. The most familiar are those of the pulmonate land snails, which usually have two sets of tentacles on the head: when extended the upper pair have eyes at their tips; the lower pair are chemoreceptors.
Olfactory receptors (scales and holes) on the antenna of the butterfly Aglais io, electron micrograph Olfactory receptors on the antennae bind to free-floating molecules, such as water vapour , and odours including pheromones .
The head bears four tentacles; the upper two are larger and bear eye-like light sensors, and the lower two are tactile and olfactory sense organs. The snail extends the tentacles by internal pressure of body fluids, and retracts all four tentacles into the head by invagination when threatened or otherwise retreating into its shell.
Cornu aspersum (common garden snail) Stylommatophora is an order [3] of air-breathing land snails and slugs, terrestrial pulmonate gastropod molluscs. This taxon includes most land snails and slugs. Stylommatophorans lack an operculum, but some close their shell apertures with temporary "operculum" made of calcified mucus.