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

1. The segmentation of the Earthworm is both external and internal.

2. The Earthworm’s blood does not contain haemoglobin.

3. Flowing through the epithelial vessels the blood absorbs carbon dioxide and gives off oxygen.

4. The Earthworms are asexual.

5. The Earthworm has a respiratory system.

6. The ventral nerve cord, the nerve belt and the nerves are the component parts of the Earthworm’s nervous system.

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

1. … covers the body protecting it from injury.

2. The two characteristics features of the nervous tissue are … .

3. The cells of the intestine walls excrete … .

4. By means of … oxygen is fed to all the organs.

5. Blood flows from … into … vessel.

6. The excretory organs are … .

7. Fertilized eggs develop inside … which forms … .

8. The organs of digestion are arranged in the following order: … .

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

1. What tissues does the Earthworm have?

2. What is the structure of the digestive system?

3. What does the circulatory system consist of?

4. What is the means of excretion?

5. Where do fertilized eggs develop?

6. Why are the annelids considered more highly developed than flatworms and round-worms?

7. What are the common features of worms?

8. What groups are worms divided into?

4. Translate a passage into Russian in written form. Text 13 mollusca

Animals Included in the Phylum Mollusca. The word mollusc means literally "soft-bodied". Over 80,000 species of molluscs have been described, including such familiar forms as the oysters, snails, slugs, and devilfish. Molluscs differ from the annelids and from the phyla above them in that their bodies are not segmented. They show bilateral symmetry.

The range in the size of the molluscs is considerable. Some forms are microscopic while the largest, the giant squid, may reach 20 feet in length.

The members of this phylum are usually protected by a shell covering therefore, many molluscs, such as clams, oysters, end scallops are known commonly as "shellfish". Various snails and their relatives have elaborately coiled shells. The garden slug is actually a snail which has lost its shell entirely. In all cases, the shell is secreted by the mantle, which is a fold of the dorsal body wall.

The ventral part of the mollusc body forms a muscular foot, which is modified in various ways, according to its function. In some forms, the foot is used for plowing through mud, in others for swimming, and in still others for gliding over hard surfaces. In squids and devilfish, the foot is modified to form long tentacles, equipped with sucking disks.

Molluscs occur in both fresh and salt water, and some live on land. The aquatic forms may often be found living in or on wharf piles, attached to rocks, or buried within the sand. Some of them, however, are fresh-swimming. The forms that live on land are found for the most part under rocks. Some of them have adopted parasitic habits.

Pearl Mussel. Natural History and Behaviour

Pearl Mussel is the common name of an animal which has a hard shell that is divided into two parts. The Pearl Mussel lives on the sand-banks of rivers and in river beds. It spends most of its life half-buried in the mud usually fixed to one spot.

The water flowing past washes the oblong shell and supplies the animal with oxygen and its food - tiny organisms and decaying organic matter.

The Shell

The bodies of the Pearl Mussel and of all the other molluscs are soft. They have no rigid skeleton. The body is protected by a hard shell composed of two valves. The valves are joined together by a pair of transverse muscles. When they contract the valves close.

The valves are opened by means of a hinge ligament, which connects them at the posterior end. As soon as the transverse muscles relax, the hinge separates one valve from the other.

The dorsal border of the valves is equipped with a system of hard, interlocking ribs and teeth. Their function is to make the contraction quite firm.

The shell consists of three layers. The outer horney layer is dark, matching the colour of the ground on which the animal rests most of the time. In the middle is the white, opaque calcareous layer. The third layer is built up of nacre or mother-of-pearl, and is beautifully irridescent. The shell provides reliable protection and a solid base for the soft body of the pearl Mussel. The shell may be regarded as the exoskeleton of the mollusk.

The Mantle

The shell is built by a fold of membrane hanging on both sides from the back of the animal's body. This is called the mantle and is a characteristic organ of the mollusc. The right and left halves fit the valves of the shell closely. Along the outer edge of the mantle, owing to the continual secretion from it, there is a constant increase in the size of the horny, calcareous and nacre layers.

The Foot

The Pearl Mussel moves about by means of a broad flat foot attached to the underside of its body. This foot protrudes between the valves and is anchored in the sand almost all the time. Separating the particles of the ground the foot acts like a wedge. It contracts its muscles and so draws the rest of the body forward.

Respiration

The space between the body of the mussel and the mantle is known as the mantle cavity. There, on either side of the body and above the foot, are the gills, two dark-brown plates with transverse stripes. The gills perform the function of respiratory organs, absorbing oxygen which is dissolved in the water.

The gills are covered with a great number of tiny cilia. Owing to the action of the cilia, water is continually drawn in and passed out.

Water flows into the mantle cavity through a narrow, posterior orifice bordered by the soft, slimy mantle fringe. This orifice is called the lower (ventral) or inhalant siphon. The other orifice, situated above the first, is called the upper (dorsal) or exhalant siphon. Water flows through the gills, bringing dissolved oxygen and removing carbon dioxide.

Nutrition

Particles of plant end animal matter get into the mantle cavity with the incoming water. The movements of the cilia direct them to the lips and the mouth.

Organs

The Pearl Mussel, like the Earthworm, has organs of digestion, a blood circulatory system and organs of excretion and reproduction, the activity of which is regulated by the nervous system. The nerve centres continually react to impulses from outside. You will see this if you put a thin twig between the valves of the shell. The Pearl Mussel will react to the irritation by pressing the parts of its shell so closely together that you will be able to pull it out of the water with the twig.

Tasks

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

1. The Phylum Mollusca includes only oysters, scallops and clams.

2. Mollusca occur in salt water.

3. Pearl Mussel is the common name for all molluscs.

4. The bodies of all molluscs are rigid.

5. The Pearl Mussel moves by means of cilia.

6. Molluscs have organs of digestion, excretion and reproduction.

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

1. The members of this phylum are … .

2. … and still others for gliding over hard surfaces.

3. The dorsal border of the valves … .

4. … a great number of tiny cilia.

5. The movements of the cilia direct them … .

6. … to pull it out of the water with the twig.

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

1. What species are included in the Phylum Mollusca?

2. What features are typical for Mollusca?

3. What do you know about Pearl Mussel?

4. What does the shell of molluscs consist of?

5. How does the Pearl Mussel move?

6. How does respiration occur?

7. How does the nerve system react to impulses from outside?

4. Translate a passage into Russian in written form.