Most sea snails have a lid-like part, called an operculum, which serves to close the entrance. Snails crawl along by a large, muscular foot. As the muscles ripple, a lubricating slime is secreted to help the snail glide over any type of terrain. They can slide over sharp glass and up walls or plants in this way. The snail's head is actually a part of the foot.
Most land snails have two pairs of tentacles, whereas aquatic snails generally have just one pair.
Eyes are either at the base or the tips of the upper tentacles. The little eye bulge is quite visible in most land snails. Vision is poor. The lower tentacles are usually smaller and are generally used to probe the surface. These provide information regarding smell and touch.