Helix pomatia:organs of sense Light The eyes of the Vineyard snail are in the upper pair of the tentacles.They are visible as small black dots. 1.digitate ganglion 2.collar cell 3.olfactory nerve 4.tentacle retractor muscle 5.lateral processed cell 6.lateral oval cell 7.optic nerve 8.accessory retina 9.lens 10.retina retinal cell: 11.microvilli 12.pigment cell 13.light sensitive cell Tentacle with eye of a slug,but similar to that of H.pomatia
The eyesight of a snail is very poor,they can at least see impressions of light.When it is light the snail fixates his sight on one point and goes there in a straight line. When it is dark however the snail crawls in a curling line.Because the eyes are on tentacles above the body snails have an angle of vision of about 90 degrees. Experiments show that Vineyardsnails can see objects as far as 7-8 cm.
Feeling,smelling and tasting Vineyard- and other snails use the lower pair of tentacles for feeling.When crawling this hangs down just above the ground.They also use the upper pair for feeling if there are no obstacles in the way. The most sensitive part of the body is the head,tentacles and mouth,and the fringes of the sole. Research show that H.pomatia can smell and is also able to distinguish between different flavors.The cells of the senses of smell are divided over the whole body,but the highest concentration is in the front part.The snail can smell something from as far as 40 cm. Like the cells of the senses of smell,the cells of the senses of taste are divided over the whole body.Especially around the mouth and the small tentacles. They can distinguish between sweet,bitter and salty.
Nerve system The central nerve system of snails consists of paired nerveknots or ganglia.They have different functions. The cerebral ganglia for the senses in the head,the buccal ganglia for the mouth,the pedal ganglia for the muscles in the foot,the pleural ganglia for the mantle,and the intestinal ganglia for the organs. A seperate,not paired, ganglia is located under the intestines, this is named the visceral ganglion.The ganglia are connected lengthwise,and there are also connections across the body. The pallial cavity's nerve knots are called pleural ganglia.The lateral ganglia are called the parietal ganglia.