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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]
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 - Well-developed lens eye of Eustrombus gigas on eyestalk has a black iris.
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.
A representation of the external and internal anatomy of a common air-breathing land snail such as Helix aspersa. Air-breathing land snails have a well-defined head with two or four sensory tentacles with eyes at the tips of the upper pair, a ventral foot, and a shell. The viscera are grouped in a hump that is contained within the spiral shell.
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.
The sensory organs of gastropods include olfactory organs, eyes, statocysts and mechanoreceptors. [23] Gastropods have no hearing. [23] 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 upper surface of head and foot has a reticulate pattern in grey and the foot is rimmed with orange. The head bears two pairs of retractable, dark-coloured tentacles, the upper pair, with the eyes on their tips, being twice as long as the lower pair. There is a dark line leading from between the tentacles along the nape of the neck. [1]
Stylommatophora is the most diverse group of land snails and slugs. Pallial cavity forms a spacious, air-filled lung. Anus is located on the right side close to the pneumostome. Operculum is missing. Two pairs of tentacle are retractable and the posterior pair bears eyes on the tips. Radula typically has many small, quite uniform teeth per row.