Text 14 molluscs and the damage they do to the agriculture

Roman Snail

The Roman Snail is a land animal. Its shell is considerably thinner than that of the Pearl Mussel and has the shape of a spiral cone. It is active in the warmer and moister seasons of the year. It creeps slowly about the trunks and leaves of the trees by extending the anterior end and lower (ventral) surface of its body (known as the foot).

At the anterior end of the snail are a mouth and two pairs of horns, or tentacles, a short and a long one. The shorter tentacles act as feelers and also to scent food; at the end of each of the longer ones is a black dot - the eye. The snail is very "short-sighted". It cannot distinguish colours: everything looks gray. The mantle cavity performs the function of a breathing organ, a lung.

In the snail's mouth is a tongue-like organ, the radula. It is equipped with several rows of sharp, strong teeth with which it eats into leaves. Destroying grapevines end leaves, the snail does great damage to plants.

One way to combat snails is to pick them off the trees when they hibernate. It is also possible to spray the plants with lethal poisons.

The Grey Slug

Grey Slugs also seriously damage garden plants and crops. In late summer representatives of the group of molluscs are often seen on edible mushrooms. In autumn they invade grain fields and vegetable gardens to feed on the young tender shoots of the winter crops and maturing cabbages. Some of them live through the winter, and can be found in early spring. Like the snail it has a pair of long tentacles und another pair of snort ones. The ends of the longer tentacles carry the eyes. Slugs distinguish objects at shot distances, but are "colour-blind". The shorter tentacle acts as feelers touching objects and food. The slug is able to move around by means of its foot.

The slug is protected from excessive dehydration, by a thick layer of slime. When the air is dry and the weather hot, slugs hide under logs, boards, or stones, coming out as darkness falls to search for food. In the autumn the animal deposits small clusters of eggs in moist soil under boards or stones, or some other shelter. The eggs are ball-shaped greenish, semi-transparent, and the size of a pin-head. It is not difficult to find them in the vegetable or flower gardens in spring or autumn under different objects, some of which have been mentioned above.

Slugs increase especially rapidly when the summer is wet and warm, and the autumn is long. In such seasons they can cause very serious damage.

To combat slugs dust the places where they conceal themselves during the day and where they lay their eggs with super-phosphate or freshly-slaked time. On contacting the skin of the slugs these substances give rise to ulcers, and the animals die.

Conclusion

If you compare a Pearl Mussel, a Snail and a Slug, you will notice that they are similar in structure. Their bodies are soft and unsegmented. They have a shell (sometimes only a remnant), a mantle, and a foot. Since the body structure of these animals is more complex than that of the worm they must have made their appearance on the surface of our planet at a later period than it did. Molluscs mostly live in the sea. Many are edible, or can be used as fish bait or food for aquatic fowl and other birds and animals hunted by man. Precious pearls develop within the shells of certain Molluscs, particularly oysters. The most valuable pearls come from the waters bordering Asia. A pearl is built around some foreign substance, as sand grains or small animal parasites, which get into the shell of the mollusc. The "mother-of-pearl" is produced by several species of molluscs. Some molluscs are harmful to man. Teredo, the snip worm damages piers, ships, and wharves by boring tunnels within them. The oyster drill bores through the shells of various edible molluscs and eats away soft parts. Snails and Slugs destroy garden plants, grapevines and crops.

Tasks

1. Write down whether the following statements are true or false. Give extensive answers.

1. The shell of the Roman Snail is thicker than that of the Pearl Mussel.

2. The shorter tentacles of the Roman Snail carry the eyes.

3. The snail doesn’t damage the plants.

4. Slugs don’t distinguish objects.

5. Slugs increase rapidly in hot summer.

6. Precious pearls develop within she shells of all molluscs.

2. Complete the sentences using the text and translate them into Russian.

1. It creeps slowly about the trunks and leaves … .

2. … the function of a breathing organ, a lung.

3. It is equipped with several rows of sharp … .

4. … touching objects and food.

5. In autumn the animal deposits … .

6. … and where they lay their eggs with superphosphate or fleshly-slaked lime.

3. Answer the following questions on the text in written form.

1. How does the Roman Snail looks like?

2. What is the way to combat Snails?

3. What and how do the Grey Slugs damage?

4. Why are the Grey Slugs lined by a thick layer of slime?

5. How do they reproduce?

6. What can you notice when comparing a Pearl Mussel, a Snail, a Slug?

7. Why are any Molluscs harmful to man?

4. Translate a passage into Russian in written form.