Characteristic features of the flatworm type. There are no organs of the respiratory system. Free-living flatworms: feeding, movement and excretion

22.09.2019

Flatworms have acquired unique features in the process of evolution. Brief description type of flatworms:

three-layer;
bilateral symmetry;
differentiated tissues, organs.

endoderm (inner layer);
mesoderm (middle layer);
ectoderm (outer layer).

Type of flatworms, classes:

tape;
gyrocotylides;
ciliary;
trematodes;
Monogenaeans;
cestodoformes;
aspidogastra.

Characteristics and examples of common representatives of the class

Fact! Third world countries are unsuccessfully trying to overcome the invasion, while in more developed societies, cases of self-infection with flatworms to reduce body weight have already been recorded.

Organ system

Names of organs

Features
There are enough worms in nature, it is only important to know about those that pose a danger to humans. For example, the marine flatworm Turbellaria is a beautiful species of primordial invertebrate often found in salt waters. The body cavity of turbellarian flatworms, like many other representatives of the class, does not have internal sections, blood, or a gas exchange system, but is equipped with powerful longitudinal and transverse muscles.

Another amazing view- planarians. Predators that can go hungry for up to 12 months, significantly decreasing in volume and “eating” themselves. They can retain signs of life even when their mass and volume are reduced by 250-300 times. But as soon as a favorable period begins, individuals develop to normal sizes.

STRUCTURE OF FLAT WORMS

CLASS cilia worms

CLASS FLUKES

CLASS TAPPEWORMS

LIST OF REFERENCES USED

Introduction

The type of flatworms includes three-layered, bilaterally symmetrical animals. Their body is built from derivatives of three layers: ecto-, ento- and mesoderm. The body wall is formed by a skin-muscular sac, the body cavity is filled with parenchyma.

Nervous system represented by nerve ganglia located at the anterior end of the body - cerebral ganglia and nerve trunks extending from them, connected by jumpers.

The sense organs are usually represented by individual skin cilia - processes of sensory nerve cells. Some free-living representatives of the type, in the process of adapting to living conditions requiring a wide variety of movements, acquired primitive organs of vision - photosensitive pigmented eyes and organs of balance.

Excretory system It is represented by a system of branched tubules ending in the parenchyma with stellate cells with a bunch of cilia. The tubules communicate with the external environment through excretory openings.

There are no respiratory or circulatory systems; gas exchange and transport of substances throughout the body are carried out through diffusion.

Flatworms- hermaphrodites; reproductive system consists of gonads - testes and ovaries - and complex system ducts that serve to excrete germ cells.

Class Ciliated worms

Most eyelash worms are free-living animals that, as a rule, lead a predatory lifestyle. They eat many protozoa (ciliates, rhizomes, flagellates), nematodes, small crustaceans, mosquito larvae - often larger animals than themselves. Some forms attack their fellow creatures. Hydra with its protective stinging cells is also subject to their attacks.

The number of species of ciliated worms reaches 3 thousand. These are marine or freshwater animals; some species live in soil, in moist habitats.

The body of worms is covered with epithelium with many cilia. The movement of the cilia, on the one hand, is the result of the beating of the cilia of the outer epithelium, on the other, a consequence of the contraction of the skin-muscular sac. These worms both crawl and swim.

In the process of digesting food in ciliated worms, as well as in coelenterates, intracellular digestion occupies a large place. Food particles, previously processed by the secretion of the pharyngeal glands, enter the intestine and are captured by intestinal epithelial cells, in which numerous digestive vacuoles are formed.

Ciliary worms are distinguished by their high regenerative ability. Thus, even a hundredth part of their body is capable of being restored into a whole animal.

Wide famous representative class - milky white planaria lives in silty parts of ponds and streams, usually on the underside of stones and other underwater objects. Its body is elongated, reaching a length of 1.5 cm, leaf-shaped and usually devoid of any appendages. Only a few ciliated animals have small tentacle-like projections at the anterior end of the body.

Class Flukes

The class of flukes includes about 4 thousand species.

Class Tapeworms

The class includes about 3 thousand species.

When sexually mature, they live in the small intestine of vertebrates; larval forms live in the body cavity and inside various organs of invertebrates and vertebrates.

1. V.B. Zakharov, N.I. Sonin "Biology": textbook for educational institutions, Moscow 2008.

(Protostomia). Representatives of the class of ciliated worms live in salty and fresh waters; some species have adapted to life in moist terrestrial habitats. Representatives of other classes lead an exclusively parasitic lifestyle, parasitizing various animals, both vertebrates and invertebrates. Currently, about 25,000 species have been described, with more than 3,000 species in Russia.

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The body is bilaterally symmetrical, with clearly defined head and caudal ends, somewhat flattened in the dorsoventral direction, major representatives- strongly flattened. The body cavity is not developed (with the exception of some phases of the life cycle of tapeworms and flukes). Gases are exchanged across the entire surface of the body; respiratory organs and blood vessels are absent.

Coverings of the body

The outside of the body is covered with single-layer epithelium. In ciliated worms, or turbellarians, the epithelium consists of cells bearing cilia. Flukes, monogeneans, cestodes and tapeworms lack ciliated epithelium for most of their lives (although ciliated cells may be present in larval forms); their integument is represented by the so-called tegument, in a number of groups bearing microvilli or chitinous hooks. Flatworms with tegument belong to the group Neodermata. Flatworms can regenerate 6/7 of their body.

Musculature

Under the epithelium there is a muscle sac, consisting of several layers of muscle cells that are not differentiated into individual muscles (a certain differentiation is observed only in the area of the pharynx and genitals). The cells of the outer muscle layer are oriented transversely, while the cells of the inner layer are oriented along the anterior-posterior axis of the body. The outer layer is called the circular muscle layer, and the inner layer is called the longitudinal muscle layer.

Throat and gut

In all groups, except cestodes and tapeworms, there is a pharynx leading to the gut or, as in the so-called intestinal turbellaria, to the digestive parenchyma. The intestine is blindly closed and communicates with environment only through the mouth. Several large turbellarians have been noted to have anal pores (sometimes several), but this is the exception rather than the rule. In small forms the intestine is straight, in large ones (planaria, flukes) it can be highly branched. The pharynx is located on the abdominal surface, often in the middle or closer to the posterior end of the body, in some groups it is shifted forward. Cestode and tapeworms have no intestine.

Nervous system and sensory organs

The nervous system is represented by nerve ganglia located in the anterior part of the worm’s body, cerebral ganglia and nerve columns extending from them, connected by jumpers. The sense organs are usually represented by individual skin cilia - processes of sensory nerve cells. Some free-living representatives of the type, in the process of adaptation to living conditions, acquired light-sensitive pigmented eyes - primitive organs of vision and organs of balance.

Nephridia and accumulation buds

Osmoregulation is carried out with the help of protonephridia - branching channels connecting into one or two excretory channels. The release of toxic metabolic products occurs either with fluid excreted through protonephridia, or through accumulation in specialized parenchyma cells (atrocytes), which play the role of “storage buds”.

More than 12.5 thousand species of flatworms are known. They are grouped into three classes: ciliated, or turbellarians, flukes and banded.
The appearance of the first flatworms is attributed to the Proterozoic and is associated with the acquisition of a number of aromorphoses: 1. Multicellularity and the formation of three layers of the body wall: ecto-, ento- and mesoderm; formation of a skin-muscle sac. 2. Differentiation of cells into large number cell types. 3.Bilateral symmetry. 4. The appearance of the anterior end of the body with a complex of sensory organs: vision, smell, touch. 5. The emergence of a nervous system consisting of lateral nerve trunks connected to each other by numerous constrictions. 6. Formation of the digestive system, including the anterior and middle sections, providing cavity digestion. 7. The appearance of an excretory system consisting of individual cells - protonephridia. 8. Formation of permanent gonads - the reproductive system. (V.B. Zakharov. Biology. Reference materials. M., 1997)
ECOLOGY OF FLATWORMS
Class Eyelash worms

The class Ciliated worms has about 3,000 species living in marine and fresh water bodies, rarely in soil. A representative of free-living ciliated worms is white (milk) planaria, living in fresh water bodies (Fig. 26.1). Planaria has a leaf-shaped body 1-2 cm long, with a widened anterior and pointed posterior end.
The body of the planaria is formed by a skin-muscular sac, covered with single-layer ciliated epithelium. Between the epithelial cells there are skin glands that secrete mucus, a type of skin glands - Rhabdites - perform a protective function. Under the epithelium there are three layers of muscle fibers (circular, diagonal and longitudinal). Due to the contraction of the skin-muscular sac and the beating of the cilia, the planaria can swim in the water column and crawl along the substrate.

The digestive system consists of the foregut and midgut, ending blindly. The mouth is located on the ventral side and leads into the ectodermal pharynx, which passes into the midgut of endodermal origin. The intestine has three main branches, from which cecal appendages arise. The digestive system is closed blindly, so the mouth opening serves to throw out undigested residues. Digestion of food is carried out intracellularly and extracellularly thanks to enzymes that are secreted by glands located in the pharynx and intestinal walls.
For the first time, eyelash worms appear excretory system. It is represented by two channels, each of which opens outward at one end. These channels branch repeatedly and give rise to narrower tubules ending in large stellate cells, which are located in the parenchyma. Stellate cells absorb fluid from the parenchyma. On the inner surface of these cells, a bundle of cilia extends into the lumen of the tubule. Vibrations of the cilia promote a constant flow of fluid into the tubules and further along the tubules through the ducts to the excretory pores. This excretory system is called protonephridial. It performs the functions of osmoregulation and removal of dissimilation products.
Nervous system consists of a cluster of nerve cells of the head ganglion (node) and nerve trunks extending from it. Her main feature- concentration of nerve elements at the head end. Between adjacent nerve trunks there is a system of thin jumpers. This ladder type structure of the nervous system. V The sense organs are represented by primitive eyes, the organs of balance - statocysts (closed sacs with pebbles of lime carbonate inside). The skin contains tactile cells.
Reproduction Planaria can occur asexually and sexually. Asexual reproduction is carried out by transverse division of the body into two parts. Division begins by transverse constriction of the body behind the pharynx. Each half regenerates missing body parts.
Sexual The ciliated worm system is hermaphroditic; it is complex. Sperm are produced in numerous testes, and eggs are produced in paired ovaries located in the front of the body. The ovary is connected by a short oviduct to the spermatheca, in which fertilization occurs. The ducts of the vitelline and shell glands open into the oviducts, the secretion of which is necessary for the formation of the cocoon. Cross fertilization. Small planarians develop in the cocoon. Ciliated worms probably evolved from phagocytella-like X ancestors
Class Flukes
Life cycle liver fluke: 1 - adult from the bile ducts of the liver of cattle, 2 - egg, 3 - miracidium (in the external environment), 4 - development of larval stages in the body of the intermediate host - the small pond snail, 5 - free-swimming cercaria, 6 - adolescaria encysted on the grass.
The representative of flukes is liver fluke Its dimensions are 3 - 5 cm. It lives as an adult in the bile ducts of the liver, in the gall bladder of herbivores and in humans. The body shape is leaf-shaped. At the anterior end of the body and on the ventral side there are oral and ventral suckers, with the help of which flukes are held in the host’s body.
The skin-muscle sac consists of epithelium, devoid of cilia, and three layers of muscles.
The digestive system is represented by a mouth located at the anterior end of the body, a muscular pharynx, an esophagus and a branched, blindly closed intestine.
Excretory system of protonephridial type. Central channel passes through the middle of the body and ends with the excretory pore.
The nervous system consists of the peripharyngeal nerve ring and three pairs of nerve trunks extending from it, interconnected by jumpers.
Sense organs are poorly developed. Only larvae that swim freely in water have eyes.
The liver fluke is a hermaphrodite. Sexual reproduction occurs in the definitive host. The male reproductive system consists of a pair of testes, vas deferens, merging into the ejaculatory canal, and a copulatory organ. The female reproductive system includes the ovary, vitelline, and spermatic receptacle, which open into the chamber - ootype, where fertilization and the formation of fertilized eggs occur. From the ootype, the eggs enter the uterus and are released through the opening.
Flukes are very prolific. Within a week, one individual produces up to 1 million eggs. For further development The eggs must fall into the water. In the water, the eggs hatch into larvae covered with cilia. They must then enter an intermediate host where asexual reproduction occurs.
Asexual reproduction of liver fluke larvae occurs in the body of a mollusk (small pond snail). As a result, a generation of larvae is formed, whose structure resembles an adult fluke, but differs in a muscular tail appendage. At this stage, the larvae leave the body of the pond snail and swim in the pond, and then settle on coastal vegetation. Cysts are formed, inside which the larvae remain viable for some time. With food, the larvae can enter the body of the final host (cow or human), in whose intestine the cyst shell dissolves, the larva penetrates the liver, grows and turns into an adult. A person becomes infected with liver fluke by drinking boiled pond water or eating vegetables and fruits that have not been washed in this water. To prevent the disease, there is no need to melt raw water from reservoirs.
Excretory system protonephridial type. Two excretory canals stretch along the sides of the body. In each segment, the lateral canals are connected by transverse canals.
Nervous system consists of a nerve ganglion located in the head and two lateral trunks running along the body.
The bovine tapeworm is a hermaphrodite. The segments located closer to the head do not have a developed reproductive system. As the segments grow, first the male and then the female reproductive system develops.
The male reproductive system consists of the testes, vas deferens, ejaculatory duct and copulatory organ.
The female reproductive system has a branched ovary and oviduct, which opens into the ootype. In the ootype the vitellaria also open; associated with it is an unbranched, blind-closed uterus and vagina. In the posterior (mature) segments of the tapeworm, only the branched uterus filled with eggs is clearly visible.
The segments of the bovine tapeworm can crawl out of the anus on their own. In the uterus, inside the shell of the egg, a six-hooked embryo is formed. For further development, this embryo must enter an intermediate host. This host for the bovine tapeworm is cattle. The intermediate host becomes infected by ingesting segments or eggs, which may end up on the grass with feces. In the stomach of livestock, the shells of the eggs dissolve. Larvae emerge from them and penetrate through the bloodstream into the muscles. In the muscles, the embryo turns into the next larval stage - the finca, which looks like a bubble filled with liquid, into which the head is screwed. A person eats meat that is poorly cooked and becomes infected with bovine tapeworm. In the human intestine, the head turns out of the vesicle, attaches itself to the intestinal walls with the help of suction cups, and segments begin to bud from the neck.
Sometimes a person becomes an intermediate host for pork tapeworm. This can happen when an already infected person vomits, when mature segments fall from the intestines into the human stomach: the shells of the eggs dissolve, the larvae come out of them and, through the bloodstream, enter various organs (liver, lungs, eyes, brain), where the fins are formed.
Life cycle of pork tapeworm. 1 tapeworm egg with oncosphere inside, 2- Finn, which develops in the muscles of a pig, 3- sexually mature individual, 4- mature penis

There is no body cavity, the space inside the skin-muscular sac between internal organs filled with a loose mass of connective tissue cells - parenchyma. Tissue fluid circulates between cells

The nervous system consists of a paired cephalic ganglion and several nerve trunks extending from it. These trunks are connected to each other by transverse nerve cords (commissures). Sense organs are most well developed in free-living ciliated worms, which have balance organs - statocysts. The eyes, unlike the eyes of jellyfish, are of an inverted type. All flatworms have receptors for the perception of mechanical and chemical stimuli.

The digestive system is present in turbellaria and flukes; it consists of two sections: anterior (ectodermal) and middle (endodermal). The intestine is blindly closed, there is no hindgut or anus. Cestodes do not have a digestive system.

Scheme of the structure of protonephridia:
1 - excretory channel,
2 - branching tubules,
3 - cyrtocytes (“stellate cells”),
4 - eyelashes ("flickering flame").

The excretory system is represented by individual parenchyma cells (atrocytes) and protonephridia. Protonephridia are of ectodermal origin and represent a system of branching channels that remove waste products from the body in dissolved form (see figure). On the side of the body cavity, the tubules are closed by cyrtocytes. A cyrtocyte is a large star-shaped cell with a bunch of cilia (“flickering flame”). The beating of the cilia ensures the outflow of intercellular fluid from the parenchyma into the protonephridial tubule. The tubules flow into one or two excretory canals, which open outwards with excretory pores. The accumulation of waste products occurs in atrocytes.
There is no circulatory system.

Flatworms are hermaphrodites. The reproductive system, in addition to the testes and ovaries, includes accessory structures that ensure the fertilization process, supply the eggs with the necessary nutrients and create protective shells around the egg. The development of flatworms occurs in most cases with metamorphosis, through a series of larval stages.

The type Flatworms are divided into classes: 1) Ciliated worms (Turbellaria), 2) Flukes (Trematoda), 3) Tapeworms (Cestoda), etc.

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