A basic level of
For each task, choose one correct answer from the four proposed.
A1. The outside of the body of roundworms is covered
- shell
- sink
- calcareous skeleton
- skin-muscle sac
A2. Unlike flatworms in the digestive system of roundworms there is
- pharynx
- intestines
- anal hole
AZ. Dioecious organisms include
- bovine tapeworm
- polyp hydra
- human roundworm
- liver fluke
- - - Answers - - -
A1-4; A2-4; A3-3.
Increased difficulty level
B1. Are the following statements true?
A. The respiratory organs of roundworms are the lungs.
B. The reproductive system of female roundworms includes the ovaries.
- Only A is correct
- Only B is correct
- Both judgments are correct
- Both judgments are wrong
B2. Choose three true statements. The sensory organs of free-living flatworms are
- primitive eyes
- taste buds on the tongue
- organs of touch on the integument
- chemical sense organs on the body
- inner ear
- olfactory organ in the nasal cavity
BZ. Establish a correspondence between the structural features of the animal and its belonging to a systematic group.
Features of the structure
A. Dioecious
B. Hermaphrodites
B. Have a body cavity
D. There is no anus in the digestive system
Systematic group
- Flatworms
- Roundworms
Write down the corresponding numbers in the table.
- - - Answers - - -
B1-2; B2-134; B3-2121.
Src="http://present5.com/presentation/3/175622154_135143061.pdf-img/175622154_135143061.pdf-1.jpg" alt="> Topic: Type Roundworms (Nemathelminthes) Objectives: Study"> Тема: Тип Круглые черви (Nemathelminthes) Задачи: Изучить характеристику типа, особенности строения и биологию представителей Пименов А. В. 2004!}
Src="http://present5.com/presentation/3/175622154_135143061.pdf-img/175622154_135143061.pdf-3.jpg" alt="> general characteristics Cavity type"> General characteristics of the Body Cavity type. Inside the skin-muscle sac, the primary body cavity develops, the schizocoel, which corresponds to the primary cavity of the embryo - the blastocoel. Intercellular fluid replaces the parenchyma. The internal organs are located in this primary body cavity. The digestive system consists of three sections : anterior, middle and hindgut.The anterior and hindgut are of ectodermal origin, and the middle is of endodermal origin.The anus appears and food begins to move in one direction.
Src="http://present5.com/presentation/3/175622154_135143061.pdf-img/175622154_135143061.pdf-4.jpg" alt=">General characteristics of the type The excretory system is represented by hypodermal (skin)"> Общая характеристика типа Выделительная система представлена гиподермальными (кожными) одноклеточными железами и "шейными железами". !} Nervous system consists of a peripharyngeal nerve ring surrounding the pharynx, and 6 nerve trunks extending forward and backward, of which the dorsal and abdominal ones are the most developed. Reproduction. Mostly dioecious organisms, direct development.
Src="http://present5.com/presentation/3/175622154_135143061.pdf-img/175622154_135143061.pdf-5.jpg" alt="> General characteristics of the type The appearance of roundworms was accompanied by the following aromorphoses:"> Общая характеристика типа Появление круглых червей сопровождалось следующими ароморфозами: 1. Образовалась первичная полость, схизоцель, которая сформировалась путем замещения паренхимы жидкостью. Жидкость находится под большим давлением и является гидроскелетом, выполняя опорную функцию; участвует в обмене веществ внутри организма, транспортируя различные вещества; 2. Появилась задняя кишка и заднепроходное отверстие, что позволило сделать процесс пищеварения поэтапным; 3. Произошла дальнейшая концентрация !} nerve cells, 6 nerve trunks are formed and a peripharyngeal nerve ring is formed; 4. A separation of the sexes occurred, which ensured combinative variability and genetic diversity of the descendants.
Src="http://present5.com/presentation/3/175622154_135143061.pdf-img/175622154_135143061.pdf-6.jpg" alt="> Structure and vital functions of nematodes Body shape and skin-muscle sac. Body whole, non-segmented,"> Строение и жизнедеятельность нематод Форма тела и кожно-мускульный мешок. Тело цельное, несегментированное, веретеновидное или нитевидное, круглое в !} cross section, covered with cuticle on the outside. The cuticle usually reaches great thickness and strength; during the growth of the worms, it is periodically shed, then resumes. Under the cuticle is the hypodermis, which is a product of cell fusion.
Src="http://present5.com/presentation/3/175622154_135143061.pdf-img/175622154_135143061.pdf-7.jpg" alt="> Structure and vital activity of nematodes Under the hypodermis there are longitudinal muscles separated by ridges"> Строение и жизнедеятельность нематод Под гиподермой расположены продольные мышцы, разделенные валиками гиподермы на 4 ленты. При сокращении спинные и брюшные ленты действуют как антагонисты. Внутри кожно-мускульного мешка имеется первичная полость (схизоцель), она не имеет собственной мезодермальной выстилки, и в ней находятся внутренние органы тела. Полость заполнена жидкостью, которая находится под давлением и играет роль «гидроскелета» .!}
Src="http://present5.com/presentation/3/175622154_135143061.pdf-img/175622154_135143061.pdf-9.jpg" alt=">Structure and vital activity of nematodes The excretory system is unique. There is a cervical">!}
Src="http://present5.com/presentation/3/175622154_135143061.pdf-img/175622154_135143061.pdf-10.jpg" alt=">Structure and vital activity of nematodes The excretory system is unique. There is a cervical"> Строение и жизнедеятельность нематод Выделительная система своеобразна. Имеется шейная железа, представленная одной или двумя !} secretory cell, located below the front of the body. One or two canals extend from them, passing in the lateral ridges of the hypodermis. At the back they are blindly closed, at the front they are connected into excretory duct, opening with an excretory pore. On the walls of the excretory canals in the anterior part of the body there are four large phagocytic cells. They capture and accumulate residual metabolic products in the cytoplasm.
Src="http://present5.com/presentation/3/175622154_135143061.pdf-img/175622154_135143061.pdf-11.jpg" alt=">Structure and vital activity of nematodes The nervous system consists of"> Строение и жизнедеятельность нематод Нервная система состоит из окологлоточного нервного кольца, окружающего глотку и пищевод и отходящих вперед и назад 6 нервных стволов, из которых спинной и брюшной наиболее развиты. Нервная система образована небольшим числом нервных клеток, что свидетельствует о ее примитивности (у аскариды, например, нервная система состоит из 162 клеток). Органы чувств развиты слабо. Имеются органы осязания, органы химического чувства.!}
Src="http://present5.com/presentation/3/175622154_135143061.pdf-img/175622154_135143061.pdf-12.jpg" alt=">Structure and vital activity of nematodes Reproductive organs have a tubular structure. Male"> Строение и жизнедеятельность нематод Органы размножения имеют трубчатое строение. Мужские половые органы имеют форму непарной трубки, тонкая часть которой является семенником, средняя часть - семяпроводом, наиболее толстый отдел - семяизвергательным каналом, открывающимся в конечный отдел кишечника - клоаку. У самки парные яичники продолжаются в яйцеводы, которые, расширяясь, переходят в две матки, открывающиеся в непарное влагалище, заканчивающееся половым отверстием на брюшной стороне тела. Оплодотворение яиц происходит в матке.!}
Src="http://present5.com/presentation/3/175622154_135143061.pdf-img/175622154_135143061.pdf-20.jpg" alt="> Repetition What is indicated"> Повторение Что обозначено на рисунке цифрами 1 - 10? Важнейшие термины и понятия: 1. Первичная полость тела, схизоцель, псевдоцель. 2. Шейная железа. 3. !} Phagocytic cells. 4. Cloaca. 5. Infective eggs. 6. Hypodermis.
Src="http://present5.com/presentation/3/175622154_135143061.pdf-img/175622154_135143061.pdf-21.jpg" alt=">Repetition What is indicated in the figure by numbers 1"> Повторение Что обозначено на рисунке цифрами 1 - 16?!}
Task 1. “Roundworms”
Write down the question numbers and missing words (or groups of words):
The phylum Roundworms includes about (_) species. The habitats of roundworms are (_), (_), (_) and (_). Roundworms studied in the school course belong to the class (_). Roundworms are characterized by a (_) body cavity. The outside of the body of roundworms is covered with (_). The musculature of roundworms is represented by (_). (_) first appears in the digestive system. The fluid of the primary body cavity performs a number of functions: (_). The excretory system is represented by (_), (_) and (_). The nervous system is formed by (_) connected by ring bridges. Ability to regenerate (_). Roundworms are characterized by (_) cellular composition.
1. What is indicated in the figure by numbers 1 – 16?
2. What is characteristic of the digestive system of roundworms?
3. Where it opens outwards excretory system roundworms?
4. Where does the female reproductive system open to the outside? Males?
Task 4. “Organ systems of roundworms”
Draw and fill out the table:
Organ systems | Peculiarities |
Skin-muscle bag | |
Body cavity | |
Digestive | |
Respiratory | |
Blood | |
excretory | |
Task 5. “Characteristics of roundworms”
Write down the numbers of the judgments, put + against the correct ones, and – against the erroneous ones.
Main location in the human body |
|
1. Human roundworm (mature females and males) | A. Upper small intestine |
2. Pinworm (mature females and males) | B. Lower small intestine |
3. Whipworm (mature females and males) | B. Large intestine |
4. Trichinella (larvae) | D. Subcutaneous fatty tissue |
5. Rishta (mature females) | D. Skeletal muscles |
Task 8. “The most important terms and concepts of the topic”
Define the terms or expand on the concepts (in one sentence, emphasizing the most important features):
1. Primary body cavity, schizocoel, pseudocoel. 2. Cervical gland. 3. Phagocytic cells. 4. Cloaca. 5. Infective eggs. 6. Hypodermis.
Task 2. 1. 1 – dorsal nerve cord; 2 – muscle cell; 3 – muscle cell nucleus; 4 – lateral ridge of hypodermis with excretory canal; 5 – hypodermis; 6 – abdominal nerve cord; 7 – queen with eggs; 8 – primary body cavity, schizocoel; 9 – intestines; 10 – cuticle. 2. Liquid. 3. Cuticle, hypodermis, longitudinal muscles.
Task 3. 1. 1 – female genital opening; 2 – abdominal nerve cord; 3 – uterus; 4 – anus; 5 – peripharyngeal nerve ring; 6 – pharynx; 7 – ovary; 8 – dorsal nerve cord; 9 – oral opening; 10 – excretory opening; 11 – testis; 12 – spicules; 13 – male genital cloaca; 14 – phagocytic cells; 15 – lateral excretory canals; 16 – “cervical” or hypodermal glands. 2. The anus appears. 3. On the ventral side in the front half of the body. In females - on the ventral side, in the front part of the body, in males - in the cloaca.
Task 4.
Organ systems | Peculiarities |
Skin-muscle bag | Under the cuticle is the hypodermis. Then the musculature of four longitudinal muscle bands. |
Body cavity | Primary, without epithelial lining. |
Digestive | Mouth with lips, pharynx, mid and hind intestine with an anus on the ventral side of the body. |
Respiratory | Absent, energy is obtained through glycolysis, or respiration at the surface of the body. |
Blood | Absent. |
Longitudinal nerve trunks connected by ring jumpers. |
|
excretory | 1 – 2 giant cells of the hypodermis, forming longitudinal excretory canals. Excretory pore at the anterior end of the body. Phagocytic cells associated with excretory channels. |
Dioecious animals. The genital organs are tubular; females have paired ovaries, oviducts, a uterus and a genital opening; males have one filamentous testis, a vas deferens, which flows into the cloaca. |
Task 5. 1 – no. 2 – yes. 3 – no. 4 – yes. 5 – yes. 6 – no. 7 – no. 8 – yes. 9 – no. 10 – no. 11 – no. 12 – yes. 13 – no. 14 – yes. 15 – yes. 16 – no. 17 – no. 18 – yes.
Task 6. 1. Ovaries, oviducts, uterus, vagina. 2. Testis, vas deferens, ejaculatory duct, cloaca. Liver, atrium, ventricle, alveoli. 5. Secondary ingestion.enterobiasis.hours. 9. Invasive. 10. Blind and large intestine; blood. 11. On the legs in the connective tissue layer of the skin; cyclops; drinking water with cyclops infected with microfilariae. 12. Elephant; lymphatic vessels, clogging them; a mosquito that infects a person when it bites.
Task 7. 1 – AB, 2 – BV, 3 – V, 4 – D, 5 – G
Task 8. 1. A body cavity that does not have its own mesodermal lining. 2. One- or two-celled hypodermal glands with canals and an excretory pore. 3. Cells associated with the lateral excretory canals and absorbing unnecessary substances from the fluid of the primary body cavity. 4. The last section of the intestine into which the hindgut and testis open in the male roundworm. 5. Eggs in which the larvae have fully developed and are capable of infection. 6. The epithelium of the skin-muscle sac, which merges into a single cytoplasmic mass - syncytium. The hypodermis forms a multilayered cuticle (in human roundworm up to 10 layers).
These are non-segmented animals. The primary body cavity is filled with fluid. They are capable of active movement. Food for free-living species is bacteria, algae and single-celled organisms. They, in turn, feed on fish fry and small crustaceans.
Structure
The structure of roundworms suggests the presence of a cylindrical or spindle-shaped body. The cuticle covers the outside. The primary cavity is located under the skin-muscle sac.
Food enters through the mouth into the pharynx. From here it goes into the digestive tube, consisting of the foregut, middle and hind intestine. It ends with the anus. Modified skin glands are part of the excretory system.
These creatures are dioecious. They lack systems such as respiratory and circulatory systems.
Universal capabilities in terms of adaptation to conditions environment can be explained by the presence of a dense outer layer (cuticle).
The habitat of roundworms in some cases includes moss. They are able to penetrate into various parts of plants: stems, roots, tubers and leaves.
The distribution range of these creatures is wide.
Differences from other types
The structure of roundworms is somewhat different from anatomical features their flat counterparts. On cross section it can be seen that the body has the shape of a circle. It is symmetrical and elongated. The skin-muscle sac serves as a kind of wall for it. The cuticle, located on the outside, acts as a skeleton.
Muscle cells consist of two parts:
- contractile;
- plasmatic.
Representatives of roundworms have a mouth opening located in the front of the body. It is not lined with epithelium. In addition to the internal organs, there is also cavity fluid. In some species it may have toxic properties. The high pressure it creates ensures reliable support for the muscle bag. It is also important in terms of metabolism.
Reproduction
In most cases, representatives of roundworms are dioecious organisms. Thanks to this, their descendants are distinguished by genetic diversity. Individual individuals are characterized by the so-called, that is, males are not similar to females in appearance.
Development is carried out indirectly. The larval stage takes place. There is no need to change the owner. Type of fertilization - internal.
Sense organs and nervous system
Nervous system
Refers to the staircase type. It is otherwise called “orthogon”. The pharynx is surrounded by a special nerve ring. There are 6 nerve trunks that extend forward and backward. Among them, the most developed are the dorsal and abdominal ones. They are connected using jumpers.
Sense organs
They also have chemical senses, meaning worms are able to detect odors. Eyes in their most primitive form are present in free-living representatives.
There are several classes, but the most numerous are nematodes. If your child is in 7th grade, roundworms will be studied in the biology program. Traditional representatives considered at the school:
- roundworms;
- pinworms.
Roundworms. Character traits
With insufficient hygiene, invasion occurs, that is, infection. In this case, eggs enter the oral cavity from the surface of unwashed vegetables and fruits, as well as hands. All this is indicated in the subject "biology". Roundworms do not need to change hosts to develop.
After entering the intestines, the larvae emerge from the egg. They easily penetrate the mucous membrane and penetrate the bloodstream. After this, they enter the heart and then into the lungs. From here they pass into the bronchi and trachea. During this period, a person experiences a cough.
The movement of larvae can last up to 12 days. All this time they grow and change their shell several times. After being hit again small intestine they continue to grow for three months. At the end of this period, the helminths become adults. Each of them lives about 1 year.
Pinworm. Characteristics of roundworm
Another representative of the class is the pinworm. It usually lives in the large intestine. Characterized by small size. Females are larger than males and reach 12 mm. Infection is carried out in the same way as in the case of roundworm.
The main reason for the invasion is insufficient compliance hygiene. If you don't wash your hands properly after using the restroom, these types of roundworms can easily enter your body. Particular caution should be exercised when in public places.
Significance in human life and nature in general
- onion;
- beet;
- wheat;
- potato
Among these creatures you can find detritivores. The source of food for them is organic remains and humus. Such worms are directly involved in the formation of soil.
Where are nematodes found?
Finding them is not as difficult as it seems. If you suddenly find yourself out of town, go to the nearest river or lake. Pay attention to the sand on the shore. These creatures are often found in it. It also makes sense to look at growths on trees and old snags. This is also the habitat of roundworms.
Some species live in algae. Thus, they can be found almost everywhere. Each of them has its own power source. Despite this, they do not have to starve. Some dig in the sand and look for bacteria, others intensively extract juices from plants.
Roundworms also live in the forest. To spot them, you should come here in rainy weather. If you wish, you can simply take a piece of moss or lichen and place it in water. Surely you will find representatives of this type in it.
Some types of flukes pose a danger to humans due to damage to vital organs. Flukes can live inside a person for years without causing any symptoms.
Kinds
The following types of helminths are distinguished:
- roundworms (nematodes);
- tapeworms (cestodes);
- flukes (trematodes).
- liver fluke (fasciola);
- cat fluke (the causative agent of opisthorchiasis);
- Schistosoma (the causative agent of schistosomiasis).
The digestive organs of flukes form a sac with 2 blindly closed channels. They do not have a circulatory system, so nutrients distributed due to the presence of a flattened body. In some helminths (liver fluke), the intestines have many branches, due to which food moves through.
Cat fluke infection
Trematodes include the causative agent of opisthorchiasis, Opisthorchis felineus. The cat fluke has the following distinctive features:
- up to 20 mm long, 2 mm wide;
- has a pointed front part;
- has a device for fixation in organs (2 suction cups);
- is a hermaphrodite;
- does not reproduce in the body of the definitive host;
- develops with a change of 2 hosts (molluscs, carp fish);
- distributed almost everywhere;
- lives up to 25 years.
The digestive organs of the helminth are represented by the oral cavity, pharynx, esophagus, and intestines. The source of infection (also known as the definitive host) releases eggs in the feces. They end up in the ground and water. Freshwater shellfish ingest eggs and become infected. The larvae penetrate the body of their first intermediate hosts and invade fish of the carp family (carp, roach, ide, bream, gudgeon).
A person becomes infected by eating fish that has not undergone proper heat treatment. It is also dangerous to eat stroganina, fish kebabs, lightly salted foods (fish meat, caviar). This fluke lives in the human liver, biliary tract, pancreatic ducts. Acute stage The disease is manifested by the following symptoms:
- fever;
- chills;
- sweating;
- pain in joints, muscles, hypochondrium on the right;
- dyspepsia;
- rash;
- weight loss.
At chronic course the pain becomes constant. Patients complain of headache, tremor, depression, nausea, bowel dysfunction, and lack of appetite.
Schistosomes
Schistosomes live in the genitourinary system and intestines of humans. These flatworms are transmitted to humans primarily percutaneously, that is, through skin while swimming.
Active movement of schistosome larvae ensures high human susceptibility and risk of infection. Infection often occurs through ingestion of contaminated water, washing, or eating food that has been washed dirty water. Body length reaches 20 mm. Females are larger. The eggs are oval-shaped and 0.1 mm in size.
Intestinal schistosomes cause abdominal pain, diarrhea, blood in the feces, and enlarged liver.
During the acute phase of the disease, the temperature rises, cough and rash appear. Often suffers genitourinary system. Schistosomes cause dysuria ( frequent urination, with pain, burning), bleeding from the vagina, pain during sexual intercourse, the appearance of blood in the urine. In men and women, the reproductive system suffers: prostatitis, epididymitis, vesiculitis, and colpitis develop. Such flukes can cause cystitis, pyelonephritis, and infertility.
Why are they dangerous?
Thus, flukes represent a separate group of helminths that are dangerous to humans. To prevent infection, you need to wash vegetables, berries, and fruits. Do not swim in dirty ponds, do not walk barefoot on the ground in exotic countries. Drink only boiled water, wash your hands more often. You can protect yourself from opisthorchiasis by boiling or frying fish for a long time before eating it.
Characteristics and structural features of roundworms
The phylum roundworms, or nematodes, presumably originated from turbellarians. Evolving, this class acquired a peculiar structure, which is strikingly different from the structure of flatworms. This fact forces us to consider nematodes as a separate specimen of the animal world. Since the relationship of nematodes with groups higher up has not been proven, they are considered a lateral branch of the family tree of animals. This phylum has more than 10,000 species of organisms.
The general characteristics of roundworms focus on external structure. From a medical point of view, roundworms are of great interest, since only they contain forms that are pathogenic for the human body.
This unique structure allows them to crawl freely and bend their body in different directions. Characteristics of the type of roundworms show that they lack blood and respiratory system. These organisms breathe through the cover of their body.
Digestive system
The digestive system of roundworms resembles a tube, that is, it is continuous. Starting with oral cavity, gradually passes into the esophagus, then into the foregut, middle and hind intestine. The hindgut ends at the anus on the other side of the body.
Many representatives of roundworms have a terminal oral opening, in some cases it is shifted to the ventral or dorsal side.
Extraction system
Breeding system
The nematode has reproductive system With tubular structure. These organisms are heterosexual. Males have only one tube, different sections of which perform various functions. The narrowest section is the testis, which, in turn, is divided into two sections - reproduction and growth. Next is the vas deferens, and the channel for the eruption of the seed.
Females have a 2-tube reproductive system. One tube, ending in a dead end, plays the role of an ovary; it is filled with germ cells capable of reproduction. This organ flows into a larger section, which plays the role of the oviduct. The largest section of the female reproductive system is the uterus. The two uteri, connecting to each other, form the vagina, access to which is open on the front of the body.
Females and males differ significantly in external signs. Males, as a rule, are smaller and the back of the body in many is twisted towards the belly. In most species of nematodes, reproduction is viviparous - females carry an egg in the uterus until the larva hatches from it.
Nervous system
The nervous system of roundworms is a nerve ring, from which nerve trunks branch. Of these, the ventral and dorsal trunk are the most developed.
Life cycle
Nematodes in the human body cause diseases called nematodes, many of which pose a serious threat to health. There are classes of roundworms that are most common among humans.
Roundworms
The egg that the roundworm produces ends up in a person with unwashed vegetables or berries, on which they fell, respectively, from the ground. The larva hatches from the egg and begins its journey along to the human body. It has the ability to pass through the intestinal walls, penetrates the blood vessels, and enters the liver, atrium and lungs with the blood flow. To develop safely, roundworms need oxygen, so the larvae migrate to the pulmonary alveoli, and from there to the bronchi and trachea.
The waste products of roundworms are very toxic, so patients may experience severe headache, constant fatigue, outbursts of irritability. In addition, ascariasis often provokes intestinal obstruction.
Very common helminths, small nematodes white. The size of males is no more than 3 mm, females reach a length of 12 mm. Infection with pinworms can occur due to non-compliance with hygiene rules, so children who visit children most often become victims of enterobiasis. kindergarten. The patient is tormented severe itching, he scratches the skin until it bleeds, pinworm eggs remain on the hands and under the nails, after which they are transferred to objects household items and food.
The structure of roundworms of this species is such that they cling tightly to the walls of the intestine and feed not only on its contents, but also on blood. The toxins released by pinworms can cause headaches, insomnia, fatigue and dizziness, as well as allergies.
By blood vessels the crooked head enters the heart, from there to the lungs, upper Airways and throat. Together with saliva, they penetrate the esophagus, then the stomach, the destination being the duodenum. This type of nematode can enter the body in two ways - either with contaminated food and water, or by penetrating through the skin. Soon after entering the body, the patient begins to experience pain in the duodenum, indigestion, fatigue, headache, depression, impaired memory and attention are observed. With absence timely treatment this disease can be fatal.
How to combat the penetration of nematodes into the body? Preventive measures are quite simple, but nevertheless require strict adherence:
- do not neglect the rules of personal hygiene, wash your hands as often as possible hot water with soap;
- carefully process all vegetables, fruits and berries before eating (to protect yourself, you need to immerse them in boiling water for 3 seconds, or for 10 seconds in hot water, then rinse thoroughly with cold water);
- It is not recommended to use human and pig feces that have not undergone the composting process as garden fertilizer;
- cut nails of adults and children as often as possible, change bed linen and underwear daily.
Nematodes are an integral part of nature, and it is impossible to eliminate them, but with the help of simple measures you can protect yourself from their invasion of the body.
General characteristics of round and flatworms
general characteristics
Common features for the class round and flatworms are:
- Indirect life cycle. Flatworms and roundworms are born from eggs laid by hermaphrodite adults. They live almost everywhere. To complete the cycle of transformation into an adult, the larva needs to go through several stages. For various types For flatworms, this requires the presence of a so-called “intermediate” host, that is, an animal (carnivorous or domestic), mollusk or insect, in whose body the larva turns into a sexually mature unit. Only after the transformation cycle is completed do flatworms pose a danger to humans.
- Structure. Both varieties of worms lack excretory and circulatory system. Having settled in the body of the “host”, helminths secrete waste products through the mouth.
At the same time, worms are characterized by a fairly large number of differences:
Nutrition. The first thing that distinguishes representatives of both classes is the structural features of the digestive system. In flatworms, for example, the digestive tract is presented in the form of a very branched tube, but they do not have an anus. In roundworms digestive system has the shape of a tube, starting with the mouth and ending with the anus. Another feature due to which helminths of both classes differ from each other is the ability of flatworms to feed on the entire surface of the body. This mainly concerns flukes, which attach to the walls of the internal organs of a person or animal and feed on blood.
Features of reproduction. Most flatworms are hermaphrodites. This means that both male and female reproductive cells develop in the body of one individual, although this does not happen simultaneously. However, in the future adult does not require the presence of a partner to reproduce. But among roundworms there are both males and females.
Nervous system. “Do worms have brains?” is one of the most common questions on thematic forums. True, the answer to this is somewhat unexpected: worms do have some semblance of a brain. In flatworms it is represented by the so-called “brain ganglion” (a node of nerve endings), from which longitudinal trunks extend. In roundworms, the number of such trunks is much smaller, and instead of the cerebral ganglion, a peripharyngeal ring is located in the anterior part of the body.
Additional accessories. The movement of helminths inside the human or animal body is carried out thanks to the presence of special devices. For this purpose, flatworms have special hooks in the front part of the body, the number of which in adult individuals can reach fifty or more units. Not all helminths have them in roundworms. Pinworms, for example, also have hooks, but their number is much smaller than that of flukes. The latter, by the way, also have special suction cups on the head, with the help of which the helminth is attached to the walls of the internal organs.
Availability internal cavity. Another significant feature due to which helminths of both classes differ from each other is the presence of a body cavity. In flukes, it is represented by parenchyma - a formation located between the outer layer of muscle and the internal organs of helminths. Nematodes belonging to the representatives of round helminths do not have parenchyma. Therefore, they are classified as primary cavitary helminths.
The main differences between helminths are in the structural features of a number of systems, ranging from organs performing the function of respiration or excretion, and ending with the degree of protection from adverse conditions.
