Flatworms |
Roundworms |
Annelids |
|
Representatives |
eyelash worms (white planaria), flukes (liver fluke), tapeworms (bovine tapeworm) |
roundworm, pinworm, nematode |
polychaetes (nereid), oligochaetes (earthworm), leeches |
The most important evolutionary achievement (aromorphosis) |
the third layer (mesoderm) and organ systems (digestive, excretory, reproductive, nervous) appear for the first time |
the anus appears for the first time (through the digestive system) |
a closed circulatory system appears for the first time |
Body cavity (the space between the skin-muscular sac and the intestines) |
absent (filled with loose parenchyma tissue) |
primary (filled with liquid) |
secondary, whole (filled with bags of liquid) |
Digestive system |
closed, undigested residues are excreted through the mouth |
through (through) |
through (through) |
Circulatory system |
closed |
||
Layers of muscles |
three (longitudinal, transverse, oblique) |
one (longitudinal) |
two (longitudinal and circular) |
Body structure (everyone has bilateral symmetry) |
leaf-shaped or ribbon-shaped body |
the body is covered with a dense covering (multilayered cuticle) |
the body consists of separate segments, the organs of movement are parapodia or setae |
Nervous system |
nerve trunks connected by jumpers |
ventral nerve cord |
|
Reproduction |
hermaphrodites |
dioecious |
polychaete dioecious, oligochaete and leeches - hermaphrodites |
Three germ layers in the individual development of animals in the process of evolution appeared in
1) flatworms
2) annelids
3) chordates
4) coelenterates
Answer
Establish a correspondence between an animal organism and a classification group of organisms: 1) primary-cavity, 2) secondary-cavity. Write numbers 1 and 2 in the order corresponding to the letters.
A) earthworm
B) Nereid
B) medical leech
D) human roundworm
D) baby pinworm
E) onion nematode
Answer
Choose three correct answers out of six and write down the numbers under which they are indicated. Which classes of worms have a passage-type digestive system?
1) Oligochaetes
2) Polychaetes
3) Nematodes
4) Eyelash worms
5) Flukes
6) Tapeworms
Answer
Answer
2. Choose three correct answers out of six and write down the numbers under which they are indicated. What signs are characteristic of the animal shown in the picture?
1) tracheal breathing
2) excretory system of metanephridial type
3) nervous system of diffuse-nodular type
4) secondary body cavity
5) skin-muscle bag
6) circulatory system of an open type
Answer
All but two of the characteristics below are used to describe the animal shown in the picture. Identify two terms that “drop out” from the general list and write down the numbers under which they are indicated.
1) dioecious animal
2) has a closed circulatory system
3) has a whole
4) the body is divided into segments
5) lives in shallow waters in fresh water bodies
Answer
1. Establish a correspondence between aromorphosis and the type of animal in which it first appeared: 1) Annelids, 2) Arthropods
A) secondary body cavity
B) dismemberment of the body into different segments
C) division of the body into two or three sections
D) circulatory system
D) ventral nerve cord
E) exoskeleton made of chitin
Answer
2. Establish a correspondence between the characteristics and the types of animals for which they are characteristic: 1) Annelids, 2) Arthropods. Write numbers 1 and 2 in the order corresponding to the letters.
A) outer chitinous cover
B) body divided into sections
B) breathing through the entire surface of the body
D) the presence of a skin-muscle sac
D) open circulatory system
E) heart on the dorsal side of the body
Answer
3. Establish a correspondence between the characteristics and types of animals: 1) Annelids, 2) Arthropods. Write numbers 1 and 2 in the order corresponding to the letters.
A) accompaniment of growth and development by molting
B) the presence of chitinous cover
B) the presence of a skin-muscle sac
D) segmented body structure without unification into large sections
D) open circulatory system
Answer
4. Establish a correspondence between the characteristics of animals and the types: 1) Annelids, 2) Arthropods. Write numbers 1 and 2 in the order corresponding to the letters.
A) closed circulatory system
B) body parts differ in structure and size
C) there is a skin-muscle sac
D) limbs have joints
D) body coverings include chitin
Answer
Establish a correspondence between the listed characteristics of animals and the animals to which these characteristics relate: 1) honey bee, 2) earthworm. Write numbers 1 and 2 in the correct order.
A) the circulatory system is not closed
B) breathes through the surface of the skin
B) has an exoskeleton
D) has compound eyes
D) hermaphrodite
E) the body is divided into equal segments
Answer
Match the animals with their characteristics: 1) earthworm, 2) leech. Write numbers 1 and 2 in the correct order.
A) lives in moist soil
B) there is a girdle on the front third of the body
B) feeds on blood
D) there are suckers on the anterior and posterior ends of the body
D) feeds on plant debris
E) saliva contains hirudin
Answer
1. Establish a correspondence between the trait and the type of worms for which it is characteristic: 1) flatworms, 2) annelids
A) the body is usually leaf- or ribbon-shaped
B) the digestive system ends at the anus
C) there is parenchyma in the space between the organs
D) the circulatory system is closed
D) the presence of a secondary cavity - coelom
Answer
2. Establish a correspondence between aromorphoses and the types of animals for which they are characteristic: 1) Annelids, 2) Flatworms. Write numbers 1 and 2 in the order corresponding to the letters.
A) secondary body cavity
B) differentiated digestive tube
B) excretory system
D) circulatory system
D) ventral nerve cord
E) the presence of parenchyma between organs
Answer
3. Establish a correspondence between aromorphoses and the types of worms in which they first appeared during evolution: 1) Annelids, 2) Flats. Write numbers 1 and 2 in the order corresponding to the letters.
A) circulatory system
B) digestive system
B) ventral nerve cord
D) excretory system
D) skin-muscle sac
E) secondary body cavity
Answer
Establish a correspondence between the type of organism and its characteristics: 1) human roundworm, 2) earthworm. Write numbers 1 and 2 in the order corresponding to the letters.
A) has a multi-layered cuticle
B) has light-sensitive cells
B) leads a free-living lifestyle
D) there is a larval stage of development
D) detritivore
E) dioecious
Answer
Establish a correspondence between the characteristics and types of worms: 1) earthworm, 2) bovine tapeworm. Write numbers 1 and 2 in the order corresponding to the letters.
A) closed circulatory system
B) lack of a digestive system
C) the spaces between organs are filled with parenchyma
D) anus
D) secondary body cavity
E) head with four suckers
Answer
Establish a correspondence between the sign of worms and the type for which it is characteristic: 1) flatworms, 2) roundworms, 3) annelids
A) the body has a leaf- or ribbon-like shape
B) have a ventral nerve cord
B) the body is inarticulate, with dense covering
D) there is a circulatory system
D) the spaces between organs are filled with connective tissue (parenchyma)
E) the body cavity is not divided by partitions
Answer
Establish a correspondence between the characteristics and the types of worms for which they are characteristic: 1) Roundworms, 2) Flatworms, 3) Annelids. Write numbers 1-3 in the order corresponding to the letters.
A) the presence of a primary body cavity
B) the presence of only longitudinal muscles
B) the presence of a ventral nerve cord
D) the presence of a circulatory system
D) leaf-shaped or ribbon-shaped body
E) filling the spaces between organs with connective tissue (parenchyma)
Answer
Answer
Choose three correct answers out of six and write down the numbers under which they are indicated. An animal that has the nervous system shown in the figure is characterized by the following characteristics:
1) the body is segmented
2) three-layer animals with bilateral body symmetry
3) there is no body cavity, the spaces between organs are filled with parenchyma
4) mixed body cavity
5) closed circulatory system
6) the digestive system does not have an anus
Answer
Choose two correct answers out of five and write down the numbers under which they are indicated. If an animal has formed the digestive system shown in the figure, then this animal is characterized by
1) closed circulatory system
2) primary body cavity
3) scalene nervous system
4) the presence of ciliated epithelium
5) gill breathing
Answer
Choose three correct answers out of six and write down the numbers under which they are indicated. Flatworms are characterized by the presence
1) anus
2) intestines
3) lungs
4) gills
5) two nerve trunks
6) hermaphroditism
Answer
Choose one, the most correct option. In which group of animals does the circulatory system transport nutrients throughout the body?
1) Annelids
2) Flatworms
3) Coelenterates
4) Roundworms
Answer
Choose one, the most correct option. Blood from an earthworm
1) fills the gaps between organs
2) flows in blood vessels
3) pours into paired excretory tubes
4) from the body cavity enters the intestines
Answer
Choose three correct answers out of six and write down the numbers under which they are indicated. Which of the following animals are classified as flatworms?
1) human roundworm
2) white planaria
3) bovine tapeworm
4) earthworm
5) liver fluke
6) onion nematode
Answer
Establish a correspondence between the features and the types of animals for which they are characteristic: 1) Roundworms, 2) Flatworms. Write numbers 1 and 2 in the order corresponding to the letters.
A) the body is flattened in the dorso-abdominal direction
B) only longitudinal muscles are present
C) most species are hermaphrodites
D) the spaces between organs are filled with parenchyma
D) the intestine ends at the anus
Answer
Choose three correct answers out of six and write down the numbers under which they are indicated. What signs are characteristic of free-living representatives of the type Flatworms?
1) leaf-shaped body
2) stinging cells
3) skin-muscle bag
4) attached lifestyle
5) active movement
6) diffuse type nervous system
Answer
Answer
Establish a correspondence between the characteristics and representatives of classes such as Flatworms. Write numbers 1 and 2 in the order corresponding to the letters.
A) sense organs are reduced
B) the body is covered with ciliated epithelium
B) anaerobes
D) hunts using a retractable throat
D) well developed cuticle
E) free-living organism
Answer
© D.V. Pozdnyakov, 2009-2019
Flatworms belong to the group of three-layered animals. In addition to the ecto- and endoderm, the embryos of flatworms develop a third germ layer - mesoderm. During development, these three leaves form the tissues and organs of the worms' body.
Flatworms have bilateral (two-sided) symmetry; only one plane can be drawn through their body, dividing the body into symmetrical halves. With bilateral symmetry, the body is distinguished between right and left halves: ventral and dorsal sides, anterior (head) and posterior (tail) ends. These signs are a consequence of aromorphoses that occurred in the ancestors of flatworms. Flatworms are protostomes.
The body of flatworms has a leaf- or ribbon-like shape and is always flattened in the dorsoventral direction, which gave rise to the name of the type. The body wall is formed by a skin-muscle sac. It consists of a layer of epithelium covering the outside of the body, and continuous layers of muscle underlying it. The outer layer is represented by circular muscles, the inner layer is longitudinal. Between them there are usually diagonal muscles. Contraction of the muscular elements of the skin-muscular sac provides the characteristic “worm-like” movements of flatworms.
The internal organs are immersed in loose connective tissue of mesodermal origin - parenchyma containing numerous cells. The functions of the parenchyma are diverse: it has a supporting role, serves to accumulate reserve nutrients, and plays a role in metabolic processes. Since parenchyma fills the space between organs, flatworms are called cavityless, parenchymatous animals. They do not have a body cavity.
The excretory system in flatworms is represented by excretory organs - protonephridia. Their function is to remove intracellular breakdown products (dissimilation products) from the body. The latter are excreted from all cells of the body and enter the intercellular spaces of the parenchyma. From here they are extracted by special cells with a “flickering flame”, i.e. with a bunch of eyelashes. Inside these cells, the tubules of the excretory (excretory) system begin. The beating of the cilia drives waste products through the tubules. Coming together, these tubules form increasingly larger tubes that flow into the paired (right and left) canals of the excretory system, which merge together and open outward into the excretory pore.
Flatworms are hermaphrodites. The reproductive system consists of the gonads (testes and ovaries) and a complex system of canals that excrete reproductive products.
Animals belonging to the type of flatworms are characterized by:
- three-layer, i.e. development of ecto-, ento- and mesoderm in embryos;
- the presence of a skin-muscle sac;
- absence of a body cavity (the space between organs is filled with parenchyma);
- two-sided symmetry;
- body shape, flattened in the dorsoventral (dorsoventral) direction;
- the presence of developed organ systems: muscular, digestive, excretory, nervous and reproductive.
The phylum flatworms (Plathelminthes) includes 6 classes. Will be discussed here
- Class ciliated (Turbellaria)
- Class flukes (Trematodes)
- Class tape (Cestoidea)
Class ciliated (Turbellaria)
About 1,500 species of ciliated worms or turbellarians are known. Turbellaria are distributed in all parts of the globe. Most species live in the seas, where flatworms apparently first arose. Freshwater and soil species are known. Almost all turbellarians are predators. They eat protozoa, worms, small crustaceans and insects. There are intestinal forms, as well as species with straight and branched intestines. Typical representatives of ciliated worms are planarians.
A small (10-15 mm long) leaf-shaped worm that lives in ponds and low-flowing reservoirs. Planaria can be found on pieces of wood rotting underwater, fallen tree leaves and plant stems.
Body coverings and movement apparatus. The body is covered with cilia. The body wall of planaria, like all flatworms, is formed by skin and muscles, which, tightly fused, make up a skin-muscular sac. Single-celled mucous glands are developed in the skin. Muscles are represented by fibers arranged in three layers (circular, oblique and longitudinal). This allows planarians to move and change their body shape somewhat.
No body cavity. Inside the skin-muscle sac between the organs there is spongy parenchyma tissue, consisting of a mass of cells, the small spaces between which contain tissue fluid. It is associated with the movement of nutrients from the intestines to all parts of the body and the final waste products to the excretory organs.
Digestive system. The mouth is located on the ventral side, in the middle or in the posterior third of the body. The digestive system consists of an anterior section - the ectodermal pharynx, and a middle section, which has the appearance of highly branched trunks ending blindly. Undigested food remains are expelled through the mouth. In ciliated worms, along with extracellular digestion, intracellular digestion plays an even greater role. Some planarians have no intestine and digestion is carried out only by phagocytic cells. Aintestinal tubellaria are of considerable phylogenetic interest (see below).
Excretory system. Protonephridia begin deep in the parenchyma as stellate-shaped terminal or terminal cells. The terminal cells contain tubules with a bunch of cilia that oscillate like a candle flame. Hence their name - flickering, or ciliary, flame. Terminal cells flow into tubules, the walls of which already consist of many cells. These tubules are numerous and permeate the entire body. They open into lateral canals, which have a large lumen, and, finally, communicate with the external environment through excretory pores. Protonephridia perform the functions of osmoregulation and removal of dissimilation products from the body. Terminal cells absorb tissue fluid from the parenchyma. The flickering flame promotes its movement through the channels to the excretory pore.
Nervous system. In ciliated worms, at the head end there is a paired cerebral ganglion and nerve trunks coming from it, of which two lateral trunks, consisting of nerve cells and their processes, reach the greatest development. The transverse trunks are connected by ring bridges, due to which the nervous system takes on the appearance of a lattice.
Sense organs still primitive. They are represented by tactile cells, which the skin is rich in, one or several pairs of pigmented ocelli, and in some, balance organs - statocysts.
Reproduction. Planarians are hermaphrodites with a complex reproductive system. They have widely developed asexual reproduction and well-defined somatic embryogenesis. Thanks to this, they serve as classical objects for studying regeneration processes.
Origin. The question of the origin of eyelash worms has not been completely resolved. The most widely accepted hypothesis is V.N. Beklemisheva (1937). He believes that the oldest turbellarians are the intestinal ones. According to his hypothesis, they originated from the planula-shaped (i.e., similar to the planula - the larva of coelenterates) ancestor of flatworms, which switched to crawling. This way of life contributed to the separation of the dorsal and ventral sides of the body, i.e., the formation of bilateral symmetry.
According to the hypothesis of A.V. Ivanov (1973), the lower intestinal turbellariae evolved directly from the phagocytella, bypassing the coelenterates. According to his concept, coelenterates are a side branch of the animal world.
Flatworms are a type of relatively simple, segmented, soft-bodied invertebrate, bilaterally symmetrical animals that do not have a body cavity (space between organs). This group includes 25,000 species. Of these, more than 3,000 are found in Russia. Most of them parasitize the body of humans and other mammals, but there are also free-living species.
Representatives of the type Flatworms are characterized by the fact that in the process of evolution they acquired three layers, bilateral symmetry, differentiated tissues and organs.
The three-layer structure is that during the process of embryonic development, three germ layers are formed in the animal: endoderm (inner), mesoderm (middle) and ectoderm (outer).
Classification
The phylum Flatworms are divided into 7 classes:
- Tape;
- Gyrocotylides;
- Cilia;
- Trematodes;
- Monogenea;
- Cestodoformes;
- Aspidogastra.
The table below discusses the features and most common representatives of these groups.
Table 1
Due to this way of life, their nervous system and sensory organs are practically undeveloped, and there is no digestive system.
They have a thick body. At the posterior end there is a special disc-shaped organ for attachment - the haptor.
They have powerful muscles and cilia to facilitate movement. Well developed sense organs.
They have a leaf-shaped form.
There is no digestive system. The nervous system is not very well developed.
They have an attachment disk, which is located on the ventral side. It consists of several rows of suction cups.
They have a special attachment organ - a rosette, which is located at the back.
Reasons for the increase in infection cases
In developed countries:
In less developed countries:
- people often cannot afford the energy resources needed to adequately cook food;
- poorly designed water supply and irrigation systems that provide additional distribution channels;
- unsanitary conditions and the use of human feces to fertilize the soil and enrich fish farm ponds;
- Some medications become ineffective and continue to be used.
While poorer countries are still struggling with unintentional infections, in developed countries cases of deliberate self-infection with tapeworms have been reported among dieters desperate for quick weight loss.
Pests
New Zealand planaria (Arthurdendyus triangulatus) eating earthworms In north-west Europe including the British Isles, there is concern about the spread of the New Zealand planaria (Arthurdendyus triangulatus) and the Australian worm Australoplana SANGUINEA, which prey on earthworms, which may lead to deterioration of soil quality. A. triangulatus is believed to have reached Europe in containers of plants imported from botanical gardens.
Human use
Two species of planarians have been successfully used in the Philippines, Indonesia, Hawaii, New Guinea and Guam to control the population growth (introduction) of the African snail species Achatina gigantea, which has begun to displace native snails in these areas. The number of unwanted snails has decreased, but it is not known exactly what role the spread of planarians played in this. Although it is believed that this has had a greater effect than other biological methods, there are now concerns that these planarians themselves could become a serious threat to their native snails.
Free-living species
Structural features
table 2
|
Organ system name |
Organs |
Peculiarities |
| Nervous | Nerves, nerve trunks, ganglion | Develops from the ectoderm. The nerve ganglion is located in the head of the animal. Six nerve trunks extend from it. Two of them pass through the belly, two through the back, one on the left side and one on the right. All nerve trunks are connected to each other by jumpers. Nerves depart from them, as well as directly from the ganglion, going to all tissues and organs. |
| Digestive | Mouth, pharynx, intestines of a blind-closed type | Develops from endoderm. Both the absorption of food and the elimination of waste from the body occurs through the mouth, which is located on the front of the body on the ventral side. The intestine consists of two sections: the foregut and the midgut. The Tape class does not have this system. |
| excretory | Protonephridia | These are specific organs characteristic only of worms. Develop from mesoderm. Constructed of branching tubules, at the ends of which there are star-shaped cells immersed in the parenchyma. They are called flickering or fiery. They are designed to capture liquid waste from the parenchyma and transfer it along the cilia to the tubules. The latter end in pores on the surface of the worm. Through them, waste is released from the body. |
| Reproductive | Ovaries, testes (simultaneously in one organism) | Develops from mesoderm. Testes are male reproductive glands. They are responsible for the production of seminal fluid containing sperm. The ovaries are the female reproductive organs. They are responsible for the production of eggs. In some representatives of the phylum Flatworms, these organs are divided into two compartments: the vitellarium and the germarium. The first one is also called zheltochnik. So-called yolk balls, rich in nutrients, are formed in it. The germarium produces eggs that are capable of development. This type of ovary produces exolecithal, or complex, eggs, which include an egg and several yolk globules under a common membrane. All flatworms, with the exception of some flukes, are hermaphrodites. They have cross fertilization, that is, different individuals exchange seminal fluid. |
| Skin-muscle bag | Epithelium, muscles | Develops from the ectoderm. The epithelium consists of a single layer of cells. On its surface there may be cilia, microvilli or chitinous hooks. The first are found in representatives of the class Ciliated worms. Microvilli and hooks are present in tapeworms, cestode-like worms and others. |
| Blood | Absent. |
Initial level of knowledge:
Response plan:
- General characteristics of flatworms
- External and internal structure of flatworms
- Reproduction of Flatworms
- Classification of Flatworms, variety of species
- Peculiarities of the structure and development of worms of the Ciliate class using the example of the Milk planaria
- Features of the structure and development of worms of the class Flukes using the example of the Liver fluke
- Features of the structure and development of worms of the Tapeworm class using the example of the Bull tapeworm and others.
General characteristics of flatworms
Number of types: about 25 thousand.
Habitat: They live everywhere in humid environments, including the tissues and organs of other animals.
Structure: Flatworms are the first multicellular animals in which, during the course of evolution, bilateral symmetry, three-layer structure, and real organs and tissues appeared.
Bilateral(bilateral) symmetry - this means that an imaginary axis of symmetry can be drawn through the animal’s body, with the right side of the body being a mirror image of the left.
During embryonic development in three-layer animals have three layers of cells: outer - ectoderm, average - mesoderm, internal – endoderm. From each layer certain organs and tissues develop:
the skin (epithelium) and the nervous system are formed from the ectoderm;
from the mesoderm - muscle and connective tissue, reproductive and excretory systems;
from the endoderm - the digestive system.
In flatworms, the body is flattened in the dorso-abdominal direction, there is no body cavity, the space between the internal organs is filled with mesoderm cells (parenchyma).
Digestive system includes the mouth, pharynx and blind intestine. Absorption of food and excretion of undigested residues occurs through the mouth. Tapeworms have a completely absent digestive system; they absorb nutrients over the entire surface of the body, being in the intestines of the host.
excretory organs – protonephridia. They consist of thin branching tubules, at one end of which there are flame (flickering) cells star-shaped, immersed in the parenchyma. A bunch of cilia (flickering flame) extends inside these cells, the movement of which resembles the flickering of a flame (hence the name of the cells). Flame cells capture liquid decay products from the parenchyma, and cilia drive them into the tubule. The tubules open on the surface of the body as an excretory pore, through which waste products are removed from the body.
Nervous system ladder type ( orthogon). It is formed by a large head paired nerve ganglion (ganglion) and six nerve trunks extending from it: two on the ventral side, two on the dorsal and two on the sides. The nerve trunks are connected to each other by jumpers. Nerves extend from the ganglion and trunks to organs and skin.
Reproduction and development:
Flatworms are hermaphrodites. Sex cells mature in the sex glands (gonads). A hermaphrodite has both male glands - testes, and female glands - ovaries. Fertilization is internal, usually cross-fertilization, i.e. worms exchange seminal fluid.
CLASS cilia worms
Milk planaria, a small aquatic animal, the adult is ~25 mm long and ~6 mm wide, with a flat, milky white body. At the front end of the body there are two eyes that distinguish light from darkness, as well as a pair of tentacles (chemical sense organs) necessary for searching for food. Planarians move, on the one hand, thanks to the work of the cilia covering their skin, and on the other hand, thanks to the contraction of the muscles of the skin-muscular sac. The space between the muscles and internal organs is filled with parenchyma, in which they meet intermediate cells, responsible for regeneration and asexual reproduction.
Planarians are predators that feed on small animals. The mouth is located on the ventral side, closer to the middle of the body, from it comes a muscular pharynx, from which three branches of a closed intestine extend. Having captured the victim, the planaria sucks out its contents with its throat. Digestion occurs in the intestines under the action of enzymes (intestinal), and intestinal cells are able to capture and digest pieces of food (intracellular digestion). Undigested food remains are removed through the mouth.
Reproduction and development. Ciliated animals are hermaphrodites. Cross fertilization. Fertilized eggs fall into a cocoon, which the worm lays on underwater objects. Development is direct.
CLASS FLUKES
CLASS TAPPEWORMS
Bull tapeworm– a tapeworm, reaches a length of 4 to 12 meters. The body includes a head with suckers, a neck and a strobila - a band of segments. The youngest segments are located at the neck, the oldest are sacs filled with eggs, located at the posterior end, where they come off one by one.
Reproduction and development. The bovine tapeworm is a hermaphrodite: each of its segments has one ovary and many testes. Both cross-fertilization and self-fertilization are observed. The posterior segments, filled with mature eggs, open and are excreted with feces. Cattle (intermediate host) can swallow eggs along with grass; in the stomach, microscopic larvae with six hooks emerge from the eggs, which enter the blood through the intestinal wall and are carried throughout the animal’s body and carried into the muscles. Here the six-hooked larva grows and turns into Finn- a bubble containing the head of the tapeworm with its neck. A person can become infected with finches by eating undercooked or undercooked meat from an infected animal. In the human stomach, a head emerges from the finca and attaches to the intestinal wall. New segments bud from the neck - the worm grows. Bovine tapeworm secretes toxic substances that cause intestinal disorders and anemia in humans.
Development pork tapeworm has a similar character, its intermediate host, in addition to pigs and wild boars, can also be humans, then finches develop in its muscles.
Development broad tapeworm is accompanied by a change of two intermediate hosts: the first is a crustacean (Cyclops), the second is a fish that has eaten the crustacean. The definitive host may be a person or a predator that eats the infected fish.
New concepts and terms: mesoderm, skin-muscle sac, tegument, hypodermis, reduction, protonephridia (flame cells), orthogon, strobila, ganglion, gonads, hermaphrodite, direct and indirect development, final and intermediate host, miracidium, cercaria, finna, segment, armed and unarmed tapeworm.
Literature:
- Bilich G.L., Kryzhanovsky V.A. Biology. Full course. In 3 volumes - M.: LLC Publishing House "Onyx 21st century", 2002
- Pimenov A.V., Pimenova I.N. Zoology of invertebrates. Theory. Tasks. Answers: Saratov, OJSC publishing house "Lyceum", 2005.
- Chebyshev N.V., Kuznetsov S.V., Zaichikova S.G. Biology: a guide for applicants to universities. T.2. – M.: Novaya Volna Publishing House LLC, 1998.
Flatworms- This is a group of animals in the rank of type. Currently, they include more than 20 thousand species belonging to seven classes. In terms of complexity of structure, they are considered the next key stage of evolution after the coelenterates.
The body of flatworms 1) is flattened in the dorso-abdominal direction, 2) has a head and caudal ends. Thus, flatworms have bilateral symmetry, i.e., only one plane can be drawn through them, dividing the body into two equal halves (right and left).
In the process of evolution, flattening and elongation of the body can be considered as an adaptation to the benthic lifestyle (crawling along the bottom).
During the process of individual development, flatworms develop three layers of cells - ectoderm, endoderm and mesoderm. While coelenterates have only two layers, there is no mesoderm (although there is mesoglea, which has a noncellular structure).
In flatworms, in the body between organs and tissues no cavitiesto her, i.e. they are cavityless. The internal space is filled with parenchyma cells (formed from mesoderm).
The excretory system is presented protonephridia. These are tubules, at the end of which, inside the body, there are cells of a special structure that collect dissimilation products from the intercellular substance surrounding them. Substances are removed through the channels.
The flattened body structure allows flatworms to make do with the amount of oxygen they receive through the surface of the body. They have there are no respiratory and circulatory systems.
The nervous system is no longer of a diffuse type (in the form of scattered cells forming a network), as in coelenterates. In more complex flatworms, the so-called scalene nervous system. There are head nerve ganglia, longitudinal nerve trunks (one or several pairs), which are interconnected by transverse jumpers. Branches extend from the trunks to all parts of the body. There are various sense organs, the presence of which depends on the lifestyle of the species. So planarians have primitive eyes.
Most flatworms hermaphrodites with a rather complex system of ovaries, testes, vas deferens and oviducts.
Thus, in flatworms there are four types of tissue: integumentary, muscle, connective, and nervous. These tissues form organs, which in turn make up organ systems.