Land invertebrates
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Accessed 19 Mar. 2024.
Slugs and snails 2022. Life, Land invertebrates. Retrieved 19 March 2024, from
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Life, Land invertebrates, s.v. "Slugs and snails," accessed March 19, 2024.
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Slugs and snails
Slugs and snails are gastropods, a group of molluscs with soft bodies that move about on one large foot. They move by alternately shortening then stretching their bodies. Slugs and snails have two pairs of feelers, called tentacles, on their heads: one pair for seeing and one for touch and smell. Most species feed on leaves and fungi. Unlike slugs, snails have hard shells. Snails will withdraw into their coiled shell if they are attacked.
Gastropod species
Different species of gastropods are found both on land (terrestrial snails) and the sea (sea snails)—including at the bottom of the deep ocean. There may be up to 100,000 living species of snail and slug, including about 24,000 known terrestrial species, 30,000 known marine species and about 5000 known freshwater aquatic species.
Shell
The snail has a thin calcareous (made of calcium carbonate) shell, with four or five whorls (turns). It retracts its body into its shell when it is inactive or threatened. The opening can even be sealed off with a thin skin dried mucus, helping it to keep the moisture in.
Senses
Snails and slugs have two pairs of tentacles on their heads. The upper pair are light-sensing: they have eyespots at the ends. Because snails and slugs are mainly nocturnal, the sense of vision is not highly developed. The tentacles act mainly as noses: olfactory organs, for sensing smell, are found in the tips of all four. Both pairs of tentacles can be retracted into the head, and, if broken off, can be regrown.
Digestion
The mouth is located beneath the tentacles. Most species have thousands of minute "teeth" on their ribbon-like tongue, known as a radula. Its rough surface helps them scrape food into their mouths and tear it into small, digestible pieces. Many land snails and slugs are plant-eaters (although most marine species are carnivorous). They are a food source for many other animals, including small mammals, birds, lizards, frogs and even those other species of gastropod that are carnivorous.
Movement
Both the snail and slug have a relatively large, single foot. To move, the muscle in it contracts and relaxes, producing a wave-like motion. Mucus oozes out from the underside of the foot, which lubricates the surface of the ground and thus reduces friction.
Slugs
Apart from the fact that slugs have no shell (although some have flat, internal shells), there is little difference between slugs and snails. The slug has a different lifestyle, however. Without a shell, it can squeeze itself into much smaller spaces. Because it consists mostly of water, the slug's soft, slimy body is prone to drying up, so small, damp hiding spaces are where it needs to be when the weather is dry. A snail can retreat into its shell to retain moisture, but the slug lacks that option.
Slugs eat dead leaves and decaying vegetable material and fungi. They also feed on a wide range of living plant matter and fungus. Some carnivorous species also eat dead slugs.
Slugs as prey
Slow-moving and soft-bodied, slugs are regularly preyed upon by a wide number of other animals. They are not entirely defencelesss, however. When attacked, slugs can squeeze their bodies into a tighter shape, making themselves more rigid and more firmly attached to the ground. Their slippery, unpleasant-tasting mucus makes them less edible. Some slugs can self-amputate part of their tail to help them escape.
Love darts
Most land snails and slugs are hermaphrodites: they possess both male and female sex organs. But they still need to mate with another of their kind. Many use "love darts" as part of the courtship process before actual mating takes place. Most darts are less than 5 millimetres (0.2 inch) long—actually quite long compared with the size of the animal—and are sharp and rigid.
Before mating, each slug or snail attempts to "shoot" a harpoon-like love dart into the other's body. It does not fly through the air, nor does it need to be directed into a certain place. At the right moment, the dart is simply stabbed into any part of the other animal's soft body. The dart does not introduce sperm into the body. Instead, it carries a hormone-like substance that helps more sperm survive after mating, thus increasing the chances of successful reproduction.
Consultant: Chris Jarvis