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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 ...
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.
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 .
Eyestalks are a specialized type of tentacle. Tentacles may also have olfactory organs at their ends. [3] Examples of creatures with olfactory tentacles include snails, the trilobite superfamily Asaphida, and the fly family Diopsidae. In slugs and snails, these tentacles will regrow if severely damaged, and in some species, are retractable. [1]
Most land snails bear one or two pairs of tentacles on their heads. 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.
The eyes are located at the base of the tentacles. The ctenidium (a comblike respiratory apparatus) goes along most of the length of the pallial cavity. This respiratory gill consists of 10 to 200 triangular filaments. The osphradium, the olfactory organ linked with the respiration organ, is usually relatively small.
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.
This animal is white, there are two pairs of tentacles, but eyes are lacking. [3]The shell is long and narrow, up to a maximum of 5.5 mm and a width of 1.2 mm. [4] The shell is colorless, glassy and transparent when it is fresh, a somewhat opaque milky-white when it is not fresh.