Snail

Introduction to Snail

Snail, a mollusk that bears a univalve (one-piece) shell. A typical snail shell is cone-shaped and spirally coiled. There are thousands of species of snails, no two species having shells of exactly the same shape or color. Some shells are drab, varying from gray to brown; others are brightly colored with orange, red, and yellow designs. They range in size from those barely visible to the unaided eye to shells that are two feet (60 cm) long. Snails are found in freshwater, in salt water, and on land.

A few snails have no means of locomotion and spend their lives attached to rocks or other objects; most, however, are able to move about. They creep along slowly on a large flattened foot, in most cases gliding along a layer of mucus that they secrete. Usually a snail can withdraw its body into the shell. Some snails have a hard, flat plate (called the operculum) on the rear part of the foot. When the snail withdraws into the shell, the operculum covers the opening.

A snail gets around on its foot. But it’s not the kind of foot you might be thinking of. A snail’s foot is actually a long, muscular organ that spreads out under the snail’s body.

A land snail moves forward by making a rippling motion with its foot. As it moves, the snail releases a slippery slime. The slime coats the ground under the snail. This helps the snail move along a little more easily. If you watch a snail cross a yard, you can see the trail of slime it leaves behind.

Slime or no slime, snails are very slow animals. It would take a snail moving at top speed more than a day to move from one end of an American football field to the other.

Snails have one or two pairs of tentacles, depending on the species. The eyes may be at the base or on the tips of one pair of tentacles; a few species have no eyes. Respiration is through gills or lungs, or through the mantle (a thin layer of tissue that envelops the soft parts of the body).

Snails do have eyes, but not all snails have eyes in the same spot on their bodies. A land snail has two pairs of tentacles that stick out from its head. On the tip of the two longer tentacles are its eyes. A land snail can move its tentacles up and down and from side to side to help it get the best view. But a sea snail’s eyes are located at the base of its tentacles. And they always stay in one place.

Not only do land and sea snails see things differently, but they breathe differently, too. A land snail breathes using its lung. Its lung is located in a fold in the mantle called the mantle cavity. Sea snails breathe through gills. Like fish, they use their gills to get oxygen from the water. A sea snail’s gills are located in its mantle cavity. Some freshwater snails have gills, too. Others have lungs, just like land snails. When they need to breathe air, they must come to the surface.

Some snails eat plant material, some eat other animals, and others eat both. Some snails are scavengers; others are parasites. Most snails are dioecious (an individual produces either eggs or sperm), but some species are hermaphroditic (one individual produces both eggs and sperm).

Snails eat many types of foods. Land snails mostly eat dying plants. They also eat fruits, living plants, and sometimes bark, too. Freshwater snails eat algae (AL jee) and the remains of dead animals and plants. Sea snails mostly feed on algae. Some also eat other small animals.

How do snails eat? Snails have teeth, but they are not like any teeth you’ve ever seen. Nearly all snails have radulas (RAJ u luhz). Radulas are hard, ribbonlike organs that look like tongues. Radulas contain rows of tiny teeth. Some snails have just a few teeth while others have thousands. As these teeth wear away over time, they are replaced by new ones. Snails don’t chew their food. Instead, they use their radulas to grind, grate, and tear it.

Some species of snails, such as abalones and some land snails, are edible. In some parts of Europe, especially France, land snails are raised for food. At one time a species of snail was the source for a very expensive dye known as Tyrian, or royal, purple. (This dye is now obtained synthetically.) Some species of freshwater snails play an important role in the transmission of a serious human disease known as schistosomiasis. Snails are often used in aquariums as scavengers to scrape debris from the sides of the tank. Some species of land snails can become garden pests.

Snail Mail

Nearly all mollusks have shells. Most mollusks also have organs called mantles. The mantle is thin and a bit like skin. In a snail, it lines the shell. A snail, like most other mollusks, uses its mantle to make its shell.

To make a shell, the mantle releases a liquid made up of shell materials. Gradually the liquid hardens and forms the shell. Over time, the mantle releases more of this liquid. This in turn adds to the size of the shell.

Snail shells come in many different shapes and sizes. Most snails have spiraled shells, like this tree snail. Some sea snails have shells that coil into cones. Other snails even have shells that are shaped like macaroni.

A snail crawls into its shell when it senses that an enemy is nearby. Remember, a snail is very slow. So it usually can’t escape from an enemy, such as a snake, a frog, or a bird. That’s where the shell comes in. It protects the snail from enemy attack.

Once safely curled up inside, snails can close off their shells. Different kinds of snails do this in different ways. One kind moves the hard part of its foot over the shell’s opening. Another kind spreads a layer of hardened slime over the opening. With the shell opening sealed off, the snail is safe from most attacks. It can stay sealed up like this for days or even weeks.

During long periods of heat or cold, snails may also curl up in their shell to stay moist. They hardly move and need little food or water. This state is similar to how a bear hibernates. When snails go though this process, it’s called estivation (ehs tuh VAY shuhn).

Yes, like most other snails, a land snail lays eggs. Most land snail eggs are very small. They are about the same size and shape as this: O. Over a few days, a land snail may lay around 100 eggs. But most of these eggs are eaten by predators.

A land snail lays its eggs in a small hole it digs in the soil. It covers the eggs with a mixture of dirt and slime. After about two to four weeks, the eggs hatch. The tiny newborn snails have very big appetites. They eat whatever is nearby—including what’s left of their eggshell. Some newborn snails will even eat other unhatched eggs.

Life is not easy for young snails. Very few snails live to be a year old. Most are killed by predators such as birds, beetles, and fish. Young snails that survive the tough first year still have some growing to do. They don’t become adults until they are about 2 years old.

Many sea snails, like the queen conch, lay their eggs on the floors of tropical oceans where they live. Some sea snails lay thousands of eggs over a few days. In fact, the queen conch can lay over 500,000 eggs at one time. But, like land snail eggs, most of these eggs are eaten by predators.

However, many queen conch eggs do hatch, and some of these young snails live long enough to become adults. An adult queen conch is one of the largest snails. It may grow a shell that is 1 foot (30 centimeters) long.

Periwinkles are a group of sea snails. There are many kinds of periwinkles, including the flat periwinkle, the checkered periwinkle, the marsh periwinkle, and even the zebra periwinkle. The common periwinkle lives along the shores of northern Europe and the Atlantic coast of North America. The average periwinkle is about 1 inch (25 millimeters) long and 3/4 of an inch (19 millimeters) wide.

Different kinds of periwinkles live on different parts of the shore. Some periwinkles live near the high-tide line. Others make their homes near the low-tide line. At low tide, when the water goes out, some periwinkles coil up inside their shells to stay moist. This also keeps them safe from predators. When the water returns at high tide, the periwinkles come out from their shells to graze on algae and tiny plants.

Whelks are large sea snails with hard, spiral shells. The knobbed whelk of the Atlantic coast can grow 8 inches (20 centimeters) long. The whelk often eats other mollusks.

A whelk’s main diet is clams. And whelks are experts at opening up a clam’s shell. First, a whelk grasps the clam in its foot. Next, it rubs its shell on the clam until the clam’s shell chips or cracks. Then the whelk slowly pries the clam apart until the clam’s body is exposed. Whelks eat the remains of dead animals, too.

Snails are of the order Gastropoda of the phylum Mollusca. The common edible snail is Helix pomatia.