Breathing of flatworms. How do flatworms breathe? Brief description of the type of flatworms

Initial level of knowledge:

Response plan:

• General characteristics of flatworms
• External and internal structure 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, while right side the body will be mirror-like to 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 internal organs 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 no digestive system at all. nutrients they are absorbed by 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:

1. Bilich G.L., Kryzhanovsky V.A. Biology. Full course. In 3 volumes - M.: LLC Publishing house"Onyx 21st century", 2002
2. Pimenov A.V., Pimenova I.N. Zoology of invertebrates. Theory. Assignments. Answers: Saratov, OJSC publishing house "Lyceum", 2005.
3. Chebyshev N.V., Kuznetsov S.V., Zaichikova S.G. Biology: a guide for applicants to universities. T.2. – M.: Publishing House LLC New Wave", 1998.

According to their body shape, worms are divided into three types: Flat, Round and Ringed. All worms are three-layered animals. Their tissues and organs develop from three germ layers - ectoderm, endoderm and mesoderm.

Type Flatworms and their characteristics

Type Flatworms unites about 12,500 species. In terms of their organization, they are higher than coelenterates, but among three-layered animals they are the most primitive. These animals can crawl slowly. The most characteristic feature of flatworms is their flattened body, in the shape of a long ribbon.

The figure below shows the structure of a Flatworm using Planaria as an example.

Variety of Flatworms, their main classes

Type Roundworms and their characteristics

Type Roundworms- a large group of animals with a long, round body in cross-section, which is pointed at the anterior and posterior ends. Roundworms are characterized by the presence of free space inside the body - a primary cavity. It contains internal organs surrounded by abdominal fluid. By washing the cells of the body, it participates in gas exchange and the transfer of substances. The body of roundworms is covered with a durable shell - the cuticle. This group has about 20 thousand species.

The figure below shows the structure of a Roundworm using the Ascaris as an example.

Type annelids their characteristics

Type Annelids- a group of animals whose representatives have a body divided into segments resembling rings folded one after another. There are about 9 thousand species annelids. Between the skin-muscular sac and the internal organs they have in general- secondary body cavity filled with fluid.

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Source of information: Biology in tables and diagrams./ Edition 2, - St. Petersburg: 2004.

All worms can be divided into three types (flat, annelid, round), each of which has its own characteristic features. This type refers to invertebrate animals that lack a body cavity and have bilateral symmetry.

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The main signs of the type of flatworms

• digestive;
• nervous;
• sexual;
• excretory

This type has several systems and even the rudiments of organs

Circulatory system

Not present, but the function of blood is performed by the parenchyma, consisting of connective cells. It is she who transports nutrients in the body.

Digestive system

Quite simplified, consists of a pharynx and intestines.

The pharynx is powerful and can:

• suck in;
• twist and envelop its victim.

The intestine consists of two sections - anterior and middle, most often branched. It has a closed structure, so that all undigested waste exits through the mouth. The mouth opening is located closer to the middle of the worm's body.

Free worms are mostly predators and they even have a peculiar device for capturing prey. This system is not observed in all classes; more primitive worms do not have it. For example, tapeworms feed on the entire surface.

Excretory system

The excretory system is quite large and consists of many tubules that unite and lead to excretory pores.

The parenchyma contains special cells that drive harmful substances into the tubules. For humans, these excretory products are very dangerous and toxic, along with poison.

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 with the help muscle contractions or the 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 members are aquatic. The ribbon-like body allows oxygen and metabolic end products to easily diffuse, which is very important for an animal without a circulatory system. That's his general characteristics. We will continue to consider the type of flatworms, moving on to the description nerve 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.

Host types

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 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 embeds itself 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.