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Eye of a snail. 1 - anterior chamber, 2 - lens, 3 - retina, 4 - optic nerve. 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
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
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.
Finally, the nerve cords terminate in a linked pair of visceral ganglia, which supply nerves to the remaining organs of the visceral mass. In air-breathing freshwater snails of the genus Lymnaea Lamarck, 1799 goal-directed decision-making during the hunt for food is performed by just two neuron types.
The radula is the snail's tongue, used as a rasping tool. unpaired osphradium (olfactory organ). lateral ciliated zones of osphradium; a single left hypobranchial gland (on organ at gill, which releases secretions, such as the reddish dye Tyrian purple). an unpaired ctenidium (a comblike respiratory structure in certain mollusks)
Behind them are the rhinophores, olfactory organs which often have complex forms. The middle part of the foot is the sole, used for locomotion. The sides of the foot have evolved into parapodia, fleshy winglike outgrowths.
Apple snails use the siphon in a way that is reminiscent of a human swimmer using a snorkel, except that the apple snail's siphon can be retracted completely, or extended to various lengths as needed. [6] For these freshwater snails, the siphon is an anti-predator adaptation.
Some claim insects evolved from prehistoric crustaceans, and they have secondary antennae like crustaceans, but not primary antennae. Antennae are the primary olfactory sensors of insects [7] and are accordingly well-equipped with a wide variety of sensilla (singular: sensillum). Paired, mobile, and segmented, they are located between the eyes ...