Type of flatworms, features of external and internal structure. General characteristics of the type of flatworms What are the structural features of flatworms

According to their body shape, worms are divided into three types: Flat, Round and Annelid. Although there are differences between these types, they share many common characteristics. All worms are three-layered animals. Their tissues and organs develop from three germ layers - ectoderm, endoderm and mesoderm.

Worms have anterior and posterior ends of their bodies. The right half of the worms' body looks like a mirror image of the left half, that is, it is symmetrical to it. This body symmetry is called bilateral. It arose with the development of active locomotion and is characteristic of worms and most other multicellular animals. The outer integument and muscles of the worms form a skin-muscular sac, which contains soft tissues and internal organs. Thanks to the skin-muscle sac, the worms maintain a constant body shape.

What are the structural features and life processes of flatworms?

Type Flatworms unites about 15 thousand species. In terms of their organization, they are higher than coelenterates, but among three-layered animals they are the most primitive. These animals can move slowly - crawl. The most characteristic feature of flatworms is reflected in the name of this type: their body is flattened (flattened) - in the shape of a leaf or a long ribbon.

The body of flatworms does not have an intestinal cavity. It is filled with loose connective tissue parenchyma, in which all internal organs are located. The musculocutaneous sac in flatworms, as in representatives of other types of worms, consists of skin and multilayer muscles.

A sign of a higher (compared to coelenterates) organization of flatworms is the presence of a central nervous and excretory system. However, just like in coelenterates, the mouth of flatworms performs the functions of both eating and removing undigested waste from the body.

Representatives of this type do not have respiratory or circulatory organs. Flatworms, with rare exceptions, are hermaphrodites - both male and female reproductive cells are formed in the body of one individual. Many free-living representatives of this type can also reproduce asexually - by division.

The phylum Flatworms includes the classes: Ciliated worms, Flukes, Tapeworms.

What are the structural features and lifestyle of ciliated worms?

A representative of eyelash worms is the milky white planaria. This small (1–2 cm long) worm lives in fresh water bodies. You can find planaria on the surface of plants taken out of water. It moves slowly along the surface of underwater objects. Two small dark eyes are visible at the front end of its body. In planaria, the dark, highly branched intestine is clearly visible through the skin. Planaria are predators that feed on small aquatic animals. During respiration, it absorbs oxygen dissolved in water and releases carbon dioxide. Gas exchange occurs through the thin skin of the entire surface of the body.

The excretory organs are a system of branched tubules extending from large stellate cells. Liquid harmful metabolic products are eliminated through excretory pores.

The nervous system is represented by a large accumulation of nerve cells at the anterior end of the body - the nerve ganglion, as well as nerve cords extending from it.

Most planarian species are hermaphrodites, but they can also reproduce asexually. In this case, a constriction is formed in the middle of the animal’s body and its front part is separated from the back. The head and other missing organs are formed on the back of the body. The front part restores the tail section. The process of recovery, or regeneration, occurs much more slowly in planaria than in coelenterates.

Planarians can regenerate their body from one three-hundredth of its part.

The practical significance of eyelash worms is insignificant. However, being numerous, they play a certain role as components of natural communities - biocenoses.

Organ system

Characteristic

Digestive

Blood

Absent.

Respiratory

Absent. Gas exchange occurs through all integuments of the body (two-way diffusion).

excretory

Protonephridia are a system of branching tubules that penetrate the entire body.

Most flatworms are hermaphrodites (bisexual), i.e. the same individual has both male genital organs (testes) and female genital organs (ovaries).

Sense organs

Eyes and organs of balance - in ciliated worms, flukes and tapeworms - there are no sensory organs.

Life cycle

Occurs with a change of 2 or 3 owners.

Meaning in human life

Let's look at examples .

Let's consider the comparative characteristics of classes of flatworms .

	Organs of attachment		Digestive system	Sense organs	Type of development
Ciliary		Have no cuticle		Have eyes and balance organs	No change of owners, direct
Flukes	Have suction cups		Poorly developed		With change of owners, indirect
Tape	Have suction cups and hooks	Have a cuticle	Absent		With change of owners, indirect	Liver fluke	Bull tapeworm
	The egg develops in water.	The eggs are hatched in the feces of the definitive host.
	A larva emerges from the egg.	The eggs are ingested by cattle (intermediate host) and form spherical larvae with hooks.
	The larva penetrates into the mollusk - small pond snail (intermediate host).	The larvae enter the muscles of the animal's body, where they form fins (vesicles), with the head and neck of the worm screwed inside.
	A floating tailed larva emerges from the mollusk, attaches to plants and turns into a cyst.	Human infection occurs by eating poorly cooked or fried contaminated meat.
	The cysts are ingested by animals or humans (the definitive hosts) and develop into an adult worm.	Finna enters the human body and turns into a sexually mature form.
	The adult worm reproduces sexually by laying eggs.	As the worm grows, new segments are formed. Each segment has its own reproductive apparatus, in which new eggs mature. The segments break off and come out with feces.

Used Books:
1.Biology: a complete reference book for preparing for the Unified State Exam. / G.I. Lerner. - M.: AST: Astrel; Vladimir; VKT, 2009 2.Biology: Animals: textbook. for 7-8 grades. general education Institutions. - 7th ed. - M.: Education, 2000. 3. Biology for those entering universities. Intensive course / G.L.Bilich, V.A.Kryzhanovsky. - M.: Onyx Publishing House, 2006. 4. Biology: textbook / reference manual / A.G. Lebedev. M.: AST: Astrel. 2009.
Internet resources used:
Wikipedia - the free encyclopedia

Flukes are characterized by the presence of hooks and suckers, a complex reproductive system and reduced sensory organs. And the segments of tapeworms even lack intestines, since they live in ready-to-eat food. Essentially, these animals are just sacks filled with eggs. Flatworms have a fairly simple structure based on bilateral symmetry. Its general characteristics are as follows: the right and left halves of the body are mirror-like. Free-living flatworms have a flattened body shape and only one opening in the intestine - the mouth. These organisms lack a circulatory system. Let's first talk about free-living species, describing the type of flatworms. Their general characteristics are presented below.

Free-living flatworms: feeding, movement and excretion

The ectoderm and endoderm, characteristic of coelenterates, in flatworms are separated by a third cellular layer - the mesoderm, from which muscle tissue and genital organs develop. The appearance of organ systems is a further step forward compared to the organization of coelenterates. Most free-living flatworms are aquatic organisms. They move using muscle contractions or movements of the cilia that cover their body. Predatory flatworms use the pharynx (the organ that connects the mouth opening with the intestines) when feeding: they press it against the prey and, through muscle contractions, tear off pieces of food, which then enter the intestines. Undigested food remains return to the pharynx and are expelled.

Flatworms, the structure of which we briefly examined, are the first group of animals to develop a real excretory system. It is represented by two excretory tubes that unite “flame cells” and excretory pores that open at the posterior end of the body. “Flame cells” get their name from the constantly oscillating clumps of cilia inside them that regulate water balance.

We invite you to take a closer look at an individual representative of this type, the flatworm. Its general characteristics and photos will help you imagine this interesting organism.

Procerodeslittoralis

The free-living flatworm Procerodeslittoralis reaches a length of 2 cm and lives on rocky sea coasts. It belongs to the class Turbellaria, most of whose representatives are aquatic. The ribbon-shaped body allows oxygen and metabolic end products to easily diffuse, which is very important for an animal without a circulatory system. This is its general characteristic. We will continue to consider the type of flatworms, moving on to a description of the nervous tissue and visual organs.

Nervous tissue, visual organs of free-living worms

A collection of nerve tissue at the anterior end of the flatworm's body forms the brain, to which nerve cords extend from the two primitive eyes. However, most flatworms avoid light and seek food using chemoreceptors. In experiments, they quickly respond to the smell of food spreading in the water.

Ciliated flatworms have the following structure. Their eyes are located at the head end of the body, above the brain, from which a pair of nerve cords extend. The pharynx, capable of turning inside out, opens into a branching intestine. All species are hermaphrodites, having both ovaries and testes. The genital opening leads to the genital cloaca, in which lies. Passing through the oviduct, the eggs are fed by the secretions of the vitelline.

Types of hosts

Apart from the excretory tubules and nerve cords, the segments of the tapeworm are, in essence, reproductive organs. Branched seminiferous tubules flow into the ejaculatory canal, which, together with the vagina, opens into the genital opening. The eggs, leaving the ovaries, are supplied with secretions of the shell glands and vitelline. The eggs are stored in the uterus.

Stages of tapeworm development

Fertilized tapeworm eggs, equipped with a yolk and surrounded by a protective membrane, accumulate in the uterus of the worm. Mature segments break off and are excreted along with the host's feces. Like flukes, tapeworms have one or more intermediate hosts. For example, the broad tapeworm (Diphyllobothriumlatum), found in the intestines of humans, dogs and cats and reaching a length of more than 9 m, has two intermediate hosts, while the pork tapeworm (Taenia solium) has one.

Development cycle of the broad tapeworm

The characteristics of the flatworm species (pictured above) are as follows. It has two intermediate hosts - a cyclops and one of the numerous freshwater fish of Europe, America and the Far East. The adult worm lives in the human intestine and can reach several meters in length. The end segments break off and are excreted in the feces, carrying up to 13 million eggs. daily. In the water, the egg hatches into an embryo, which is eaten by the Cyclops. In it, the embryo develops into the first larva. If the Cyclops is eaten by a fish, a second larva is formed, which is embedded in the tissue of the fish. If this contaminated and undercooked fish is eaten by a person, it is released. Using tiny hooks, the larva attaches itself to the human intestinal wall and transforms into its adult form within 3 weeks. The cycle repeats.

Pork tapeworm development cycle

So, we briefly examined the organisms that interest us and gave their general characteristics. The type of flatworms causes many problems to humans, so scientists are developing new means of combating them.

Distinctive feature flatworms- body flattened in the dorso-ventral direction. Unlike coelenterates, flatworms have between ectoderm And endoderm(outer and inner layer of cells) there is a third layer of cells - mesoderm. Therefore, they are called three-layer animals that do not have a body cavity (it is filled parenchyma- loose cellular mass in which internal organs are located).

The symmetry of the body is bilateral. There are over 12,000 species in the phylum. The type of flatworms is divided into classes: ciliary, flukes, tape worms

Class ciliated worms

Eyelash worms They live in seas, fresh water bodies and moist soil. They feed mainly on small animals. Their body is covered with cilia, with the help of which they move. One of the representatives is white planaria.

At the anterior end of the body two lateral outgrowths (organs of touch) are visible. Next to them are two eyes, with the help of which the planaria distinguishes light. Planaria is a predator. Its pharynx is a catching apparatus that protrudes outward through its mouth, located on the ventral side, penetrates the prey and sucks out its contents. Digestion of food occurs in the branched intestine. Undigested remains are expelled through the mouth. The planaria breathes over the entire surface of its body. The excretory organs consist of a system of branched tubules located on the sides of the body. Liquid harmful metabolic products are eliminated through excretory pores.

Nerve cells are collected in two nerve trunks, which are connected by thin bridges. At the anterior end of the body they form a thickening - ganglion, from which the sensory organs (eyes and organs of touch) and the posterior end of the body extend nerve spines.

The reproductive organs - two oval ovaries and numerous testes, develop in the body of one individual and form reproductive cells - eggs And spermatozoa. Animals whose bodies contain both female and male reproductive organs are called hermaphrodites. Their fertilization is internal, cross-fertilization, after which the planaria lays cocoons with eggs. Her development is direct.

Fluke class

Once in the water, microscopic larvae equipped with cilia develop from the eggs. They penetrate the body of the small pond snail mollusk, in which they grow, multiply, and tail larvae appear. These larvae leave the mollusk, actively swim in the water, then attach to plants, cast off their tail, and become covered with a thick shell - a cyst is formed. With grass or water, the cyst enters the cow's intestines, where it develops into an adult worm. A person can become infected with liver fluke if he drinks water from a dirty pond.

Class tapeworms

Tapeworms - almost all hermaphrodites, are characterized by high fertility and development with a change of hosts. Each segment of the bovine tapeworm has one ovary and many testes. The eggs mature in the oldest, posterior segments, which break off and are released with feces. Further development of the eggs will occur if they are ingested by cattle along with the grass. In the stomach of a cow, larvae emerge from the eggs, which, boring into the intestinal walls, enter the blood.

Answers to school textbooks

Structural features of flatworms:

The body is elongated and flattened in the dorsal direction, the anterior and posterior ends are clearly distinguishable;

They have bilateral symmetry, which allows for more active movements than in radially symmetrical animals (coelenterates);

There are four types of tissues: integumentary, connective, nervous and muscle;

The body wall is a skin-muscular sac formed by a single-layer ectodermal epithelium and muscles lying in three layers (outer - circular muscles, the next, deeper located - longitudinal, deepest layer - diagonal muscles);

Inside the skin-muscle sac there is loose tissue - parenchyma, which contains all the internal organs;

The digestive system is blind and does not have an anus;

The nervous system consists of two nerve ganglia in the anterior part of the body and longitudinal cords extending from them, connected by jumpers;

The excretory system is represented by branched tubules, starting in the parenchyma with stellate cells that have a cavity with a bunch of cilia located in it; vibrations of the cilia cause a flow of fluid containing metabolic products, directing it into the tubules, which communicate with the external environment through excretory openings;

The reproductive system is hermaphroditic, consists of gonads and a complex system of ducts that serve to excrete germ cells;

2. What sense organs do flatworms have?

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 primitive organs of vision - photosensitive pigment eyes and organs of balance.

3. What is parenchyma?

Parenchyma is loose connective tissue that fills the spaces between organs. Functions of parenchyma:

1) supporting;

2) storage of nutrients;

3) participation in metabolism and digestion.

In the absence of food, the parenchyma is depleted.

4. How does the nervous system of flatworms work?

The nervous system is represented by two nerve nodes located at the anterior end of the body - the cerebral ganglia and the nerve trunks extending from them, connected by jumpers, i.e., in flatworms, the nervous system is of the scalene type.

5. What are the structural features of the excretory system of flatworms?

6. How does the excretory system of flatworms work?

The parenchyma contains stellate cells that secrete water and metabolic products into the lumen of the tubules. Stellate cells have a bunch of cilia in the recess, which continuously vibrates and drives fluid out through special tubules. The tubules unite into tubes and form pores on the surface of the body. These excretory organs also regulate osmotic pressure, which is why flatworms are common in fresh waters.

7. What kind of life do eyelash worms lead?

Ciliated worms include free-living marine or freshwater worms (milk planaria, black planaria, many-eyed worms), as well as terrestrial ones. As a rule, eyelash worms are predators. They eat many protozoa (ciliates, rhizomes, flagellates), nematodes, small crustaceans, mosquito larvae - often larger animals than themselves.

8. What structural features of flukes are associated with their lifestyle?

Dense protective shell covering the body;

Two suckers for attachment to host tissues;

Hermaphroditism; high fertility;

Simplified sense organs.

9. Describe the development of the fluke.

An adult (sexually mature) individual of the liver fluke lives in the liver of large herbivorous mammals and humans, feeds mainly on bile, as well as blood and liver cells, sometimes causing the death of the main host.

10. Who is called the intermediate host? Who is the intermediate host of the liver fluke?

11. What are the structural features of tapeworms?

Structural features of tapeworms:

Ribbon-shaped body, consisting of a head, neck and several thousand segments, which increase in size towards the end of the body;

On the head there are organs of attachment to the walls of the host’s intestine (suction cups, suction slits, hooks);

Each segment contains a hermaphroditic reproductive system;

The last segments are filled with fertilized eggs, these segments are torn off and brought out;

There is no digestive system; food is absorbed over the entire surface of the body;

The nervous system is formed by the head ganglion, from which nerve trunks run along the body.

12. What is finna?

Finna is one of the stages of tapeworm development. It is a bubble filled with liquid, in the cavity of which there is a formed worm head with four suckers.

Finna enters the human intestine with uncooked or undercooked meat, Finna attaches to the intestinal wall, and the growth of a worm begins, poisoning the person with metabolic products that cause indigestion and anemia.

13. How does the development of bovine tapeworm occur?