In polychaete worms, fertilization occurs in. The value of polychaete worms. Human interaction

24.10.2019

Class Polychaetes. General morphofunctional characteristics

Type of annelids. The main features of the organization type

General characteristics of supertype Trochophores

General characteristics of coelomic animals

Subsection Coelomic (Coelomata). They have a higher level of organization than non-coelomic (Acoelomata), which include lower worms: flat, primary cavity and nemertines.

Distinctive features coelomic animals are manifested in the following:

1. Availability secondary cavity or coelom lined
epithelium of mesodermal origin. Overall – more
perfect transport system than the primary cavity
bodies and parenchyma characteristic of lower worms.

2. Structure metamerism , manifested in the repeatability
organs and structures. Metamerism captures like ectodermal
nye and mesodermal structures.

3. Development circulatory system , performing the main
way respiratory function and transport of nutrients
substances and waste products.

4. Open excretory system associated with the whole
provides not only the function of excretion, but also the regulation
water regime.

Currently, it is customary to distinguish several supertypes among coelomic animals: trochophores (Trochozoa), tentacles (Tentaculata), chaetognaths (Chaetognatha) and deuterostomes (Deuterostomia).

Supertype Trochophores (Trochozoa). Trochophore coelomic animals have a large similarity in embryonic and postembryonic development.

They tend to:

spiral fragmentation in embryogenesis,

predominantly teloblastic anlage of the mesoderm,

primacy in the formation of the mouth (from the blastopore),

during development with metamorphosis, the formation of a characteristic larva is observed – trochophores, with which the name of the supertype is connected.

The trochophores are the following types:

type Annelids (Annelida),

type Sipunculida (Sipunculida),

type Echiurida (Echiurida),

type Pogonophora (Pogonophora),

Mollusca type,

phylum Arthropoda (Arthropoda),

Onychophora type.

Type Annelids. About 12 thousand species. They live in the seas, fresh waters on land.

The main features of the organization of the type of annelids:

1. Metamerism external and internal structure. Body – worm-like, divided into segments, or segments. Many organ systems are repeated in each segment. The body of annelids consists of a head lobe, a segmented trunk, and an anal lobe.

2. Available skin-muscle sac , consisting of skin epithelium, circular and longitudinal muscles, which are lined from the inside by coelomic epithelium.

3. Overall filled with coelomic fluid, which acts as internal environment organism. In general, many functions of the body are carried out (transport, excretory, sexual, musculoskeletal).

4. Intestines consists of three functionally different sections: anterior, middle and hindgut. Some species have salivary glands.

5. For most rings closed circulatory system . This means that blood flows only through the vessels and there is a network of capillaries between arteries and veins.

6. The main excretory organs are metanephridia ectodermal origin.

7. Nervous system consists of paired cerebral ganglia and a ventral nerve cord with metamerically repeated paired ganglia in each segment.

8. Ringed worms are usually separate sexes, but hermaphroditism is often observed.

9. Development often proceeds with metamorphosis. A typical larva in sea rings – trochophore.

Progressive features: the presence of a coelom, metamerism of the structure, the appearance of a circulatory system, an excretory system like metanephridia, a more highly organized nervous system and sensory organs.

Primitive Traits: the trochophore has a primary body cavity, protonephridia, an orthogonal nervous system, and in the early stages – blind intestine.

Type Annelids opens in animal system highest level organizations are coelomic animals. This type first there is a set of all organ systems characteristic of higher groups of organisms up to mammals and humans. The features of their organization can be traced in all other types of coelomic animals. up to chordates.

Type of annelids divided into classes: class Primary rings (Archiannelida), class Polychaeta (Polychaeta), class Low-bristle (Oligochaeta), class Leeches (Hirudinea).

Class Polychaete- the central class of annelids, characterized by the largest number of species (about 8 thousand) and ecological diversity. Mostly marine free-living animals.

Polychaetes have well-separated head section with sensory appendages and limbs - parapodia with numerous bristles.

Body polychaete worms consists of a head section, a segmented trunk and an anal lobe.

Head formed head lobe (prostomium) and oral segment (peristomium). The mouth is located ventrally on the peristomium. Many polychaetes have ocelli and sensory appendages on their heads.

A - anterior part of the body; B - posterior end of the body

Picture 1 - External structure Nereids

1 - antennae, 2 - palps, 3 - peristomial antennae, 4 - eyes, 5 - prostomium, 6 - olfactory fossa, 7 - peristomium, 8 - parapodia, 9 - setae, 10 - dorsal antennae, 11 - pygidium, 12 - anal antennae, 13 - segment.

On the trunk segments there are paired lateral outgrowths with setae - parapodia. These are primitive limbs with which polychaetes swim, crawl or burrow into the ground.

Each parapodia consists of a basal part and two lobes - the dorsal (notopodium) and abdominal (neuropodium). At the base of the parapodia on the dorsal side there is dorsal mustache, and on the abdominal abdominal. These are the sensory organs of polychaetes. Often, the dorsal antennae in some species is transformed into feathery gills. Parapodia armed with tufts bristles, consisting of organic matter close to chitin. Among the bristles there are several large bristles - atsikul, to which muscles are attached from the inside, setting in motion the parapodia and a bundle of bristles.

Figure 2 - Parapodia Nereis pelagica

1 - dorsal antennae, 2 - lobes of dorsal branch of parapodia, 3 - setae, 4 - lobes of ventral branch of parapodia, 5 - ventral antennae, 6 - ventral branch of parapodia, 7 - supporting setae, 8 - dorsal branch of parapodia.

The body of polychaetes is covered with a single layer of skin epithelium, which secretes to the surface thin cuticle.

Lies under the skin circular and longitudinal muscles. The longitudinal muscles form four longitudinal bands: two on the dorsal side of the body and two on the ventral side.

Overall. When paired coelomic sacs close in each segment above the intestine and under the intestine, dorsal and abdominal mesentery, or mesentery . Between the coelomic sacs of two adjacent segments, transverse partitions are formed - dissipations. The wall of the coelomic sac, lining the inside of the muscles of the body wall, is called parietal mesoderm , and the coelomic epithelium that covers the intestines and forms the mesentery is called visceral layer of mesoderm . The coelomic septa contain blood vessels.

In general, it performs several functions: musculoskeletal, transport, excretory, sexual and homeostatic.

Digestive system consists of three departments.

Anterior section begins with a mouth opening on the peristomium from the ventral side. The oral cavity passes into a muscular throat which serves to capture food objects. Followed by the throat esophagus, in which they open salivary gland ducts. Some species have a small stomach.

middle intestine is a derivative of the endoderm and serves for the final digestion and absorption of nutrients.

Posterior intestine ectodermal origin and can perform the function of regulating the water balance in the body. Fecal masses are formed in the hindgut.

The anal opening usually opens on the dorsal side of the anal lobe.

Polychaetes mostly have skin breathing , but some species have dorsal skin gills , formed from the parapodial antennae or appendages of the head. They breathe oxygen dissolved in water. Gas exchange occurs in a dense network of capillaries in the skin or gill appendages.

The circulatory system is closed and consists of the dorsal and abdominal trunks connected by annular vessels, as well as peripheral vessels. Through the dorsal, the largest and pulsating vessel, blood flows to the head end of the body, and through the abdominal - in the opposite direction. Through the annular vessels in the anterior part of the body, blood is distilled from the dorsal vessel to the abdominal one, and vice versa in the posterior part of the body. Arteries depart from the annular vessels to parapodia, gills and other organs, where a capillary network is formed, from which blood is collected in venous vessels that flow into the abdominal bloodstream. In polychaetes, the blood is often red in color due to the presence of the respiratory pigment hemoglobin dissolved in the blood. Longitudinal vessels are suspended on the mesentery (mesenterium), annular vessels pass inside the dissipations.

Figure 3 - Scheme of a cross section of a polychaete worm

1 - epithelium, 2 - circular muscles, 3 - longitudinal muscles, 4 - dorsal antennae (gill), 5 - notopodium, 6 - supporting seta (acicula), 7 - neuropodium, 8 - nephridial funnel, 9 - nephridial canal, 10 - oblique muscle, 11 - abdominal vessel, 12 - ovary, 13 - abdominal antennae, 14 - setae, 15 - intestine, 16 - whole, 17 - dorsal blood vessel.

excretory system polychaetes represented metanephridia . Each segment contains a pair of metanephridia. Each metanephridium consists of a funnel lined with cilia and open as a whole. The movement of cilia into the nephridium drives solid and liquid metabolic products. A channel departs from the funnel of nephridium, which penetrates the septum between the segments and in another segment opens outwards with an excretory opening.

Nervous system. Paired supraesophageal ganglia form brain , which has three divisions. The brain innervates the sense organs on the head. Near-pharyngeal nerve cords depart from the brain - connectives to the abdominal nerve chain, which consists of paired ganglia, repeating segment by segment. Each segment has one pair of ganglia. When paired ganglia merge, a neural chain is formed. In some species, the nervous system is complicated by the fusion of the ganglia of several segments.

sense organs most developed in mobile polychaetes. On their heads they have eyes (2-4) non-inverted type, goblet or in the form of a complex optic vesicle with a lens. In addition, they have developed organs of smell, touch in the form of special sensory cells located on the appendages of the head and parapodia. Some species have organs of balance - statocysts.

Most polychaete worms separate sexes. Sex glands of mesodermal origin and are formed on the wall of the coelom. Sex cells from the gonads fall into the whole, where their final maturation takes place.

Some polychaetes no genital ducts and sex cells through the breaks in the body wall go into the water, where fertilization occurs. In this case, the parental generation dies.

In a number of species there are sex funnels with short channels whole products mesodermal origin, through which the reproductive products are brought out - into the water.

In some cases, germ cells are derived from the coelom through nephromixia, which simultaneously perform the function of the genital and excretory ducts.

Reproduction of polychaetes may be sexual or asexual. In some cases, metagenesis is observed.

asexual reproduction occurs by transverse division of the body of the worm into parts (strobilation) or budding. This process is accompanied by the regeneration of the missing parts of the body.

sexual reproduction often associated with the phenomenon epitokia . Epitokia is a sharp morphophysiological restructuring of the worm's body with a change in the shape of the body during the maturation of reproductive products: the segments become wide, brightly colored, with swimming parapodia.

Nereids males and females become epitonic and float to the surface of the sea to breed, after which they die or become prey to birds and fish. From eggs fertilized in water, larvae develop, settling to the bottom, from which adults are formed.

Palolo sexual reproduction is preceded by asexual reproduction, in which the anterior end of the body remains at the bottom, forming an atopic individual, and the posterior end of the body is transformed into an epitonic caudal part filled with reproductive products. The backs of the worms break off and float to the surface of the ocean. Here the reproductive products are released into the water and fertilization takes place. Epitoke individuals of the entire population emerge for reproduction at the same time, as if on a signal. This is the result of the synchronous biorhythm of puberty and biochemical communication of sexually mature individuals of the population.

In worms that develop without epitokia , males and females do not change their shape and breed in bottom conditions.

The most important features of the development of polychaetes are:

spiral, deterministic crushing of fertilized eggs,

teloblastic anlage of mesoderm,

metamorphosis with the formation of a larva - trochophore.

Manifestations of primitive features of organization at the stages of trochophore and metatrochophore (primary cavity, protonephridia, orthogon) indicate the relationship of coelomic animals with a group of lower worms.

The value of polychaete worms. The biological and practical importance of polychaete worms in the ocean is very great.

they represent important link in food chains . They are of particular importance in the nutrition of other animals, as they are absorbed without residue. Sea rings are a favorite food of fish, they occupy an important position in the trophic chains. marine ecosystems. To strengthen the food base of fish in our country, for the first time in the world, acclimatization of nereids (Nereis diversicolor) to the Caspian Sea, which were brought from Sea of Azov. This successful experiment was carried out under the guidance of Academician L.A. Zenkevich in 1939–1940. Some polychaetes are used as food by humans, such as the Pacific palolo worm (Eunice viridis).

accept participation in the purification of sea water and the processing of organic matter facilitating the biogenic cycle. Particularly diverse are the marine forms that are found on different depths up to the limit (up to 10–11 km) and in all latitudes of the World Ocean. They play a significant role in marine biocenoses and have a high density of settlements: up to 100 thousand ind. per 1 m 2 of the bottom surface.

Polychaete worms are of the phylum Annelids, thus being relatives of our common earthworms.

Habitat

Polychaete worms are long-bodied inhabitants of the sea. However, some species have adapted to living in fresh water, as well as on land - in deep soil layers.

Appearance and structure

The similarity with earthworms is found primarily in the structure of the body, which is divided into many segments. The length of polychaetes (the so-called polychaete worms in Greek) varies from 2 millimeters to three meters.

tubular polychaete marine worm photo

Segments y large species there may be several hundred. In each segment, a set of internal organs is repeated:

Whole bags;
Sexual ducts;
excretory organs.

Parapodia extend from each segment - lobe-shaped outgrowths, on which there are chitinous bristles. This feature gave the name to the whole group of worms. In some species, there is a bundle of tentacles on the head segment, which plays the role of gills.

Another feature of polychaete worms is their developed eyes, which have a complex structure. They also have a resemblance vestibular apparatus- statocysts. These are bubbles in which there are solid spherical bodies - statoliths.

polychaete worms photo

When the body changes its position, the statoliths roll over the walls of the bubble and irritate the cilia of the epithelium, the nerve impulse from which is transmitted to the central nervous system, after which the animal restores balance.

The whole variety of polychaete worms is divided into free-swimming species and sessile - attached to the bottom of the sea.

Food

Polychaete worms feed on either detritus, that is, decaying organic debris, or animal food. Sedentary species extract detritus from the water column with the help of their tentacles, which also function as gills.

polychaete ringed worm a photo

Free-swimming worms extract detritus from the ground by eating it or digging it out with their long tentacles. Predatory families polychaete worms are, for example, nereids and glycerides.

reproduction

Polychaetes in most cases are dioecious animals. However, they do not form real gonads (organs that produce germ cells). Sex cells arise from the coelomic epithelium.

Fertilization is external. The eggs hatch into larvae called trochophores. These are planktonic organisms that are microscopic in size and swim with the help of many cilia. After some time, they settle to the bottom and transform into adult animals.

lesson type - combined

Methods: partially exploratory, problem presentation, reproductive, explanatory-illustrative.

Target: mastering the skills to apply biological knowledge in practical activities, to use information about modern achievements in the field of biology; work with biological devices, tools, reference books; conduct observations of biological objects;

Tasks:

Educational: shaping cognitive culture, mastered in the process of educational activity, and aesthetic culture as the ability to have an emotional and valuable attitude towards objects of wildlife.

Developing: development of cognitive motives aimed at obtaining new knowledge about wildlife; cognitive qualities of the individual associated with the assimilation of the basics scientific knowledge, mastering the methods of studying nature, the formation of intellectual skills;

Educational: orientation in the system of moral norms and values: recognition high value life in all its manifestations, health of one's own and other people; ecological consciousness; education of love for nature;

Personal: understanding of responsibility for the quality of acquired knowledge; understanding the value of an adequate assessment of one's own achievements and capabilities;

cognitive: the ability to analyze and evaluate the impact of environmental factors, risk factors on health, the consequences of human activities in ecosystems, the impact of one's own actions on living organisms and ecosystems; focus on continuous development and self-development; the ability to work with various sources of information, convert it from one form to another, compare and analyze information, draw conclusions, prepare messages and presentations.

Regulatory: the ability to organize independently the execution of tasks, evaluate the correctness of the work, reflection of their activities.

Communicative: the formation of communicative competence in communication and cooperation with peers, understanding the characteristics of gender socialization in adolescence, socially useful, educational and research, creative and other types of activities.

Technology : Health saving, problematic, developmental education, group activities

Activities (elements of content, control)

Formation of students' activity abilities and abilities to structure and systematize the studied subject content: collective work - study of the text and illustrative material, compilation of the table "Systematic groups of multicellular organisms" with the advisory assistance of expert students, followed by self-examination; pair or group performance of laboratory work with the advisory assistance of a teacher, followed by mutual verification; independent work on the studied material.

Planned results

subject

understand the meaning of biological terms;

describe the features of the structure and the main processes of life of animals of different systematic groups; compare the structural features of protozoa and multicellular animals;

recognize organs and systems of organs of animals of different systematic groups; compare and explain the reasons for similarities and differences;

to establish the relationship between the features of the structure of organs and the functions that they perform;

give examples of animals of different systematic groups;

to distinguish in drawings, tables and natural objects the main systematic groups of protozoa and multicellular animals;

characterize the direction of evolution of the animal world; give evidence of the evolution of the animal world;

Metasubject UUD

Cognitive:

work with different sources of information, analyze and evaluate information, convert it from one form to another;

write a thesis different kinds plans (simple, complex, etc.), structure educational material, give definitions of concepts;

make observations, set up elementary experiments and explain the results obtained;

compare and classify, independently choosing criteria for the indicated logical operations;

build logical reasoning, including the establishment of cause-and-effect relationships;

create schematic models highlighting the essential characteristics of objects;

identify possible sources of necessary information, search for information, analyze and evaluate its reliability;

Regulatory:

organize and plan your learning activities- determine the purpose of the work, the sequence of actions, set tasks, predict the results of the work;

independently put forward options for solving the tasks set, foresee the final results of the work, choose the means to achieve the goal;

work according to a plan, compare your actions with the goal and, if necessary, correct mistakes yourself;

own the basics of self-control and self-assessment for making decisions and making a conscious choice in educational and cognitive and educational and practical activities;

Communicative:

listen and engage in dialogue, participate in a collective discussion of problems;

integrate and build productive interaction with peers and adults;

adequately use speech means for discussion and argumentation of one's position, to compare different points of view, to argue one's point of view, to defend one's position.

Personal UUD

Formation and development of cognitive interest in the study of biology and the history of the development of knowledge about nature

Receptions: analysis, synthesis, conclusion, transfer of information from one type to another, generalization.

Basic concepts

General characteristics of the type Annelids, concepts: parapodia, peripharyngeal nerve ring, ventral nerve cord. Closed circulatory system. Polychaetes. Bristles.. Caring for offspring.

During the classes

Knowledge update ( concentration of attention when learning new material)

Select all correct answers

1. roundworms characterized

A. flat body shape B. round body shape

C. through the digestive system D. breathing with the help of gills

2. Representatives of the class of flukes live, as a rule, in the environment

A. aquatic B. organismic C. soil D. ground-air

3. Regulation of body functions is carried out by the system

A. excretory B. nervous C. digestive D. reproduction

4. Representatives of the type of annelids are characterized

A. bristles protruding from the body wall B. skin epithelium rich in glands

C. primary body cavity D. closed circulatory system

5. The class of tapeworms includes

A. pork tapeworm B. bovine tapeworm

C. human roundworm G. sandworm

6. Tapeworms, like flukes:

A. there are no sense organs B. the body is long, ribbon-like

C. organismal habitat D. development with a change of hosts

7. The great fecundity of the liver fluke is explained

B. branched intestine

G. the possibility of reproduction at the larval stage

V. are highly prolific G. live in an anoxic environment

10. Distribute representatives of flatworms into classes

Classes Representatives

A. Ciliary worms 1) bovine tapeworm 2) cat fluke

B. Flukes 3) white planaria 4) pork tapeworm

B. Tapeworms 5) liver fluke

6) marine planaria

Learning new material(teacher's story with elements of conversation)

Type Annelids, or Ringworms

CLASS POLYCHETATES, OR POLYCHETES

General characteristics. Among various worms, annelids are the most progressive group. Its representatives are predominantly free-living worms. On their body, one can distinguish the head section, trunk and tail section. The body consists of rings - segments, the number of which varies in different species. Length per body from 0.5 mm to 3 m.

ringedworms

Ringed worms have bilateral symmetry. The body consists of three layers of cells and is divided by partitions along and across the body (Fig. 155). The internal cavity of the worm is divided by partitions into separate segments. There is liquid inside. Movement is provided by bundles of circular and longitudinal muscles, as well as special paired outgrowths of the body located on the sides of each segment - parapodia (similar to legs), which not all annelids have.

Annelids have sense organs: sight, touch, taste, smell, hearing, balance.

Most annelids have a closed circulatory system, i.e., blood does not pour freely into the body cavity, but moves only through the vessels. There is no heart, its function is performed by contracting walls of blood vessels.

The digestive system includes the mouth, pharynx, esophagus, midgut, hindgut, and anus. Breathing is carried out through the moist surface of the body or with the help of gills (Fig. 156). The excretory system is located in each segment of the body of the worms. The nervous system is characterized by an accumulation nerve cells above the pharynx - the peripharyngeal ring (this is the primitive brain) and the ventral nerve cord with branches of the nerves in each segment.

There are annelids dioecious and hermaphrodites. Reproduction is possible asexually and sexually. During asexual reproduction, the body of the worm breaks up into several parts, and then each of them completes the missing head and tail sections. Sexual reproduction occurs with the participation of two individuals, even in hermaphrodites. When they come into contact, they exchange sex cells. After fertilization, the eggs enter a special formation on the body - a girdle, which then, like a clutch, slides from the front end of the body and remains in the soil.

The type of annelids is divided into several classes, among which the most significant three are: Polychaetes, Low-bristle and Leeches.

Class Polychaetes, or Polychaetes. These worms are typically marine animals, only certain types Polychaetes live in fresh water. They got their name for the numerous bristles located on the parapodia.

Lifestyle. Most polychaete annelids lead a free lifestyle. However, among them are known living in the body of sponges, mollusks, on starfish, fish. They are found at different depths in warm and cold waters, reaching greatest variety in the coastal zone tropical seas. Many annelid polychaete worms live on seabed in large numbers, for example, in the Barents Sea, the population density of ringlets reaches 90 thousand copies per 1 m2.

ringedpolychaete

Polychaetes live among algae, reefs, in sand, soft silt, some of them build horn, sand and calcareous pipes and live in them.

Parapodia with bristles make it possible to move well in water, on the surface and in the thickness of the soil, inside the tubes.

Among the polychaete worms there are predators that feed on crustaceans, molluscs, coelenterates and worms. There are omnivores that filter water and feed on plants.

Free-living polychaetes swim all their lives in the water column, carried sea currents. Bottom rings live on the bottom of the sea and feed on organic remains. aquatic plants and animals.

Type Annelids. Class Small-bristle worms

The development of polychaetes occurs with the alternation of life forms. Their larvae do not look like adults. Each life form performs various functions: reproduction, resettlement, self-preservation. In some polychaetes, care for offspring is observed, for example, they guard laid eggs. Caring for offspring is the more active, the fewer eggs the female lays. Among the polychaetes there are viviparous.

Galileo. leeches

The palolo worm is one of the polychaete species, reaching a length of 1 m. One of the representatives of the polychaete worms of the genus Nereis was specially brought to the Sea of Azov to improve the food supply for fish.

Answer the questions

1. What are the differences in the structure of round and annelids?

2. Why did polychaetes get such a name?

3. What is the meaning of polychaetes in nature?

Independent work

1.Give a general description of annelids according to the plan.

Symmetry:

Body length and shape:

Internal structure

Sense organs:

Circulatory system:

Digestive system:

excretory system:

Nervous system:

Breeding method:

Habitat:

2.Establish the traits of adaptability of earthworms to life in the soil and name them.

Structure:

3.Specify which organs in the body earthworm perform the following functions:

digestion

removal of liquid harmful substances from the body

substance transfer

regulation of the work of organs, their relationship:

Resources

Biology. Animals. Grade 7 textbook for general education. institutions / V. V. Latyushin, V. A. Shapkin.

Active forms and methods of teaching biology: Animals. Kp. for the teacher: From work experience, —M.:, Enlightenment. Molis S. S. Molis S. A

Working programm in biology, grade 7 to the Teaching Methods of V.V. Latyushina, V.A. Shapkina (M.: Bustard).

V.V. Latyushin, E. A. Lamekhova. Biology. 7th grade. Workbook to the textbook by V.V. Latyushina, V.A. Shapkin "Biology. Animals. 7th grade". - M.: Bustard.

Zakharova N. Yu. Control and verification work in biology: to the textbook by V. V. Latyushin and V. A. Shapkin “Biology. Animals. Grade 7 "/ N. Yu. Zakharova. 2nd ed. - M.: Publishing house "Exam"

Presentation Hosting

Consider the general appearance, lifestyle, structure and organ systems of polychaete worms using the example sea worm- Nereis, which is a typical representative of this class.

General form. Nereis is a large worm up to 10 centimeters long (Fig. 36). The body of the worm is elongated and slightly flattened, it is formed by more than 150 segments. At the head end of the body are palps and tentacles, two pairs of eyes, antennae and an olfactory fossa. The body segments have paired lateral outgrowths and function as legs. At their ends there are bristles, clinging to the surface of the bottom, the worm moves. At the posterior end of the body, the trunk segments pass into the anal lobe, which contains the anus.

The body of the Nereis is covered with a thin cuticle. Two layers of subcutaneous muscles and skin form a skin-muscular sac.

Lifestyle. Nereis lives in the coastal zone of the seas at a shallow depth in mink passages that it digs in the sand. Feeds on algae and various small animals

Internal structure (Fig. 37). Directly behind the skin-muscle sac in the body of the worm there is a cavity. Unlike the cavity of roundworms, it is lined with a layer of integumentary cells and is therefore called the secondary body cavity. (Remember the name of the body cavity of roundworms and explain why.) Each segment of the body has its own isolated cavity filled with a special aqueous liquid.

The principle of creating isolated segments - compartments - is used by designers in the development of projects capital ships and submarines, where each compartment is hermetically sealed. Thanks to this, the vessel does not sink in the event of an accident in one of the compartments.

Digestive system. The intestine stretches along the entire body and consists of three sections: the anterior, middle and posterior intestines. The mouth opening opens into the pharynx, in which the teeth are located to help hold prey. The pharynx passes into a narrow esophagus. Next comes the midgut, which looks like a straight tube. It digests food. The colon opens outward through the anus.

excretory system. Each body segment has a pair of excretory canals. One end of this channel opens into the body cavity, and the other goes out.

Respiratory system. The function of the respiratory organs is performed by the dorsal antennae and skin. Blood vessels pass directly under the skin and in the dorsal antennae. This arrangement of blood vessels allows the body to remove carbon dioxide and enrich the blood with oxygen, d) "The circulatory system of Nereis consists of two vessels - dorsal and abdominal, which are connected by annular vessels. Blood circulates through the body due to the rhythmic contraction of the dorsal and anterior annular vessels.

The nervous system of the Nereis is well developed and consists of a cerebral ganglion, which has the shape of a peripharyngeal ring. Two nerve trunks depart from it along the ventral side of the body, which form thickenings in each segment.

Sense organs. The organs of vision (4 eyes) are located at the head end of the body of the worm. The function of the tactile organs is performed by antennas, palps on the head and lateral outgrowths. In addition, Nereis has olfactory pits that help the animal to feel dissolved in water. chemical substances. Eyes are the most important sensory organ of polychaete worms. If the true eyes disappear in immobile polychaete worms, ocelli of various structures appear. In worms that lead a motionless life in their armor, these interchangeable eyes do not appear anywhere, but on the gills. But this is still a trifle. Here, in some species of worms, which pass 9I, so to speak, backwards, the eyes are at the anus. You will not see this in any other animal.

Reproduction. Polychaete worms are dioecious animals, but according to appearance Male and female cannot be distinguished.

Sex glands that produce sex cells are formed in each segment of the worm, and finally these cells mature in the body cavity. From it, the germ cells through the excretory canals exit into environment where fertilization takes place. On a moonlit night, many worms leave their burrows, rise and accumulate near the surface of the sea, releasing germ cells into the water. It was then that the local population of the islands Pacific Ocean gets worms, because for him it is gourmet food.

Nereis can breed and asexually when individual segments begin to increase, gradually turning into a new organism. Sometimes a scattering or a chain of fused worms is formed, consisting of many individuals (30).

Life cycle. The larva that emerged from the egg lives in the water column. Its spherical body has no parts, it is surrounded by cilia, with the help of which the larva swims. Subsequently, it is segmented. Gradually, the larva passes to the bottom way of life. Diversity of oagatochaete worms. The class Polychaete worms, which is divided into two subclasses, has over 7500 species (Fig. 38).

The subclass Stray worms include worms that actively move and eat algae, small crustaceans, other worms, and even molluscs. The length of these worms reaches three meters. Stray worms move along the bottom or swim. In smooth species of worms, the body is transparent, at the head end contains large black eyes. The representative of this subclass is nereis.

The subclass Sitting worms includes worms whose skin secretes special substances, subsequently begin to harden, forming a transparent shell - the outer skeleton. In some worms, grains of sand or fragments of mollusk shells are attached to this shell, further compacting it. There are also such worms whose body covers are penetrated by lime, forming an outer shell - a skeleton in the form of solid tubes. The entrance to the tubes can be closed with a special cap. The body of immobile worms is not clearly divided into segments. These animals breathe with gills located at the head end of the body. Sessile worms feed by filtering out small organisms that live in the water column. famous representative of this subclass is marine sandstone, a large worm up to 30 centimeters long. Fish feed on sea sandstones.

Polychaete worms are the most large group organisms. Scientists have about 10 thousand species of the class of annelids. Common representatives: sandworm living in the Arctic, Arctic Ocean.

A distinctive feature is the numerous bristles collected in bundles located on the sides of each segment.

The body of a polychaete worm is divided into a large number of divisions, ranging from five to eight hundred pieces, but sometimes there are exceptions.

Description

Like similar worms, in polychaete worms, the body is divided into several parts:

head
long
torso
anal lobe

located at the back of the mill.

They are inhabitants of the water depths, they are covered with skin-muscular processes - organs of movement, which are called parapodia, it is with the help of them that it is possible to move forward.

The whole carcass of the worm is dressed in a muscle bag. Outside, the body is made up of a thin cuticle covering the epithelium. Under the skin of the polychaete there is a musculature consisting of longitudinal and annular muscles. Rings are from two millimeters to three meters long, and this is a fairly large value for invertebrates.

Habitat

Polychaetes mostly live in salty waters and lead a bottom lifestyle. However, there are individuals that vegetated in the zone, not located in the immediate vicinity of the bottom, these individuals include the Tomopterid family. There are also polychaetes that have adapted to fresh water, woody soil.

Food

The diet of the polychaete polychaete is relatively varied. Most feed on detritus - dead organic matter, this choice is associated with a fixed lifestyle. But there are also species that eat mollusks, coelenterates, ampictinids.

Enemies

Fish, some types of crustaceans love to eat polychaete worms, because it is tasty and healthy food. Let's talk about the use of worms for fishing by people, since this activity sharply reduces their numbers.

reproduction

Polychaete worms are heterosexual, with the exception of some hermaphrodites. The sex glands are present in both females and males. The female has eggs and the male has sperm. Due to external fertilization, a larva, a trophora, is formed from the eggs.

Trophora moves through outgrowths, sinking to the bottom, where metamorphosis proceeds into an adult. Some families of polychaete worms also reproduce asexually. There are a couple of varieties of asexual reproduction: archetomy and paratomy.

In the first case, the body is divided into dozens of segments, which later grow to a normal state, and in the second variation, everything happens exactly the opposite.

Digestive system

Worms and their system are very curious, the system responsible for receiving energy is represented by the mouth, the pharynx, which has chitinous teeth, the esophagus and the stomach. These unusual creatures have an intestine divided into three sections:

On the last part is the anal ring.

Circulatory system

Polychaetes have a closed circulatory system, each representative of annelids, that is, blood always flows through the vessels.

There are two main vessels in the camp, connected by semicircular formations: dorsal and abdominal. There is no heart, but its duties are performed by the folding of the walls of the spinal vessel and other rather big capillaries.

Nervous system

The freely moving polychaete worms have developed sense organs, expressed by two tentacles and antennae. A smaller part for polychaetes has vision and balance organs. And all this is achievable thanks to the nerve nodes and nerves that permeate the entire body.

excretory system

The withdrawal of harmful liquid occurs with the help of paired tubes located in each segment of the carcass.

Meaning, interesting facts

Despite their small size, they perform many important functions for nature:

They clean up the water
Eating decaying remains
They are food for marine life.

Lifespan

Annelida polychaete worms live for about six years.

It is interesting

All the most interesting in the world of beetles. The barbel beetle and a complete description of its way of life.

Polychaete class: structure

Class Polychaeta (polychaetes) - mainly marine worms, eg. common coastal Nereis (Nereis).

What lifestyle do polychaete worms lead

Polychaete worms are often large, active forms with a well-developed nervous system and sensory organs.

The class of polychaetes is characterized by the following features: sensitive appendages of the head lobe are well developed, in particular, there is always one pair of palps, or palps, which in sessile polychaetes are turned into a crown of tentacle-like appendages, often called "gills".

Each segment of the body bears a pair of primitive legs - parapodia, equipped with bristles.

The shape of the body of polychaetes is elongated, only slightly flattened in the dorsal-ventral direction, or regularly cylindrical. The body consists of a different number (from 5 to 800) segments (Fig. 211). By the number of segments, the forms are low-segment, or oligomeric (Dinophilus, Fig. 212; Myzostomum and their relatives), and multi-segment, or polymeric forms (most representatives of Polychaeta).

The anterior, or preoral, part of the body - the prostomium and the posterior, or anal lobe - the pygidium differ from the segments of the body and are special, non-metameric parts of the body. The segments of the body in simpler cases are completely equivalent, or homonomous, have the same look and contain approximately the same organs. Such homonomy is a sign of primitive organization and is best expressed in free-moving, vagrant forms.

Heteronomy, or the difference in value of segments in different areas of the body, manifests itself most sharply in sessile polychaetes as a result of unequal living conditions for the front part of the body, protruding from the tube, and the back, always hidden in the depths of the dwelling.

Body polychaete rings, as a rule, is equipped with various appendages that serve partly for movement, partly for sensory organs. The appendages are more strongly developed on the head section, where they have a different character than on the trunk.

The head section consists of a preoral region - the prostomium, or head lobe, and the peristomium, which carries the oral opening and represents the first segment, but is often the result of the fusion of several (2-3) anterior segments (Fig. 213). The process of cephalization - the inclusion of one or more trunk segments in the head section - is observed not only in annuli, but also in arthropods.

The most permanent and characteristic appendages of the prostomium are a pair of palps, or palps.

There is also a pair or more organs of touch - tentacles (antennas), which have a variety of sizes and shapes. On the peristomium, antennae, or cirrhi, often develop in varying numbers. The palps and antennae are innervated by the brain, while the antennae are innervated by the anterior end of the ventral nerve cord.

The body is characterized by the presence of paired lateral outgrowths - parapodia (Fig.

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Education

Polychaete worms: a brief description of the class

Polychaete worms are by far the largest group marine organisms. Most often, representatives of the class live at the bottom of a sea reservoir and much less often lead a planktonic way of life.

Polychaete worms: body structure

The body of a representative of this class consists of a head section, a long trunk and a specific anal lobe.

In most cases, the body of such an animal is clearly divided into several segments, each of which is attached to a parapodia.

Parapodia are nothing more than primitive limbs with small antennae and bristles.

Interestingly, the parapodia of some members of the group were transformed into gills.

Like other representatives of the annedil type (leeches, low-bristle worms), in such an animal the body consists of a skin-muscular sac.

From above, the body of the worm is covered with a thin protective cuticle, under which there is a single-layer epithelium. Under the skin there is a musculature, which consists of longitudinal and circular muscles, which are responsible for the movement and contraction of the animal's body.

Polychaete worms: internal structure

Representatives of this class have a fairly developed digestive system, which consists of three parts.

The anterior part consists of a mouth opening that opens into oral cavity. Then the food particle enters the muscular pharynx. By the way, it is in the pharynx that contains powerful jaws made of chitin.

Some species are even able to turn it outward.

After grinding, food enters the esophagus, where the main glands that produce saliva open. Only a few representatives have a small stomach. The midgut of the animal serves for complete digestion and absorption of essential nutrients.

The posterior intestine is responsible for the formation of feces and opens with an anus on the dorsal part of the anal lobe.

Polychaete worms have a closed circulatory system, which consists of the dorsal and ventral arteries.

By the way, the dorsal vessel is large and has contractile functions, so it works like a heart. Besides, large arteries connected by the so-called annular vessels that carry blood to the limbs and gills.

The respiratory system in representatives of this class is absent.

The organs of gas exchange are skin and gills, which are located either on the parapodia or in the anterior, head section of the body.

The excretory system consists of small metanephridia that remove waste products from the coelomic fluid during external environment. Each segment has its own pair excretory organs, which open outwards with small holes - nephropores.

As for nervous system, then it consists of a typical peripharyngeal ring, from which the abdominal nerve chain departs.

Interestingly, almost all representatives of this class have highly developed organs of touch and smell. Some species also have eyes.

Polychaete worms: reproductive system and reproduction

To begin with, it should be noted that almost all species of this group are capable of asexual reproduction, which in most cases is represented by body fragmentation, less often by budding.

Nevertheless, animals have a well-developed reproductive system.

Polychaete worms (Polychaetes)

Reproduction of worms is exclusively dioecious. Gonads form on the wall of the secondary body cavity. The release of germ cells can be carried out through tissue rupture - in this case, the adult dies.

Some representatives have specific openings through which gametes are released. Fertilization takes place in aquatic environment. A larva develops from the zygote, which outwardly bears little resemblance to an adult. Accordingly, the development of a young worm occurs with metamorphoses.

Comments

Class Polychaeta (Polychaeta)

The more evolutionarily progressive the species, the closer the chains are, one might say, merge into one.

Many mobile polychaete worms have eyes (several pairs, including eyes, are on the caudal lobe).

In addition to antennae and antennae, there are organs of touch and chemical sense on the parapodia. There are organs of balance.

Most are segregated. Usually the sex glands are present in each segment. The eggs and sperm are first in the whole, from where through the tubules excretory system or breaks in the body wall are released into the environment. Thus, fertilization in polychaete worms is external.

A trochophore larva develops from a fertilized egg, swimming with the help of cilia, having a primary body cavity and protonephridia as excretory organs (in this way it resembles the structure of ciliary worms).

Settling on the bottom of the trochophore turns into an adult worm.

There are polychaete species that can reproduce asexually (by dividing across).

Type Annelids

The most important aromorphoses of the type:

1) organs of movement appear - parapodia,

2) the first respiratory organs appear,

3) secondary cavity of the body - in general,

4) the circulatory system appears.

The circulatory system in animals can be of 2 types: closed and open.

In a closed circulatory system, blood flows only through the vessels and does not spill out of them. In an open circulatory system, there are only large vessels, they open into the body cavity.

Therefore, the blood pours out of the vessels, washes the internal organs, and then again collects in the vessels.

In annelids closed circulatory system.

For animals of this type, segmentation is characteristic - their body is divided into repeating sections - segments that look like rings.

Hence the name of the type. Moreover, the segments have exactly the same external and internal structure. And the body cavity is also divided by partitions into compartments.

The body of the worm can contain from 5 to 800 segments.

Polychaete class (Polychaeta) - full description.

Among them, only the first segment stands out, which carries the mouth and, in some, sense organs, as well as the anal lobe.

The phylum Annelids includes several classes, the most important of which are Polychaete Worms, Olichaete Worms and Leeches.

Class Polychaetes (Polychaetes)

Most polychaetes live in the seas.

They live on the bottom, where they crawl between vegetation and rocks. Among them there are also sedentary forms - they are attached to the bottom and form a protective tube around themselves.

Consider polychaete worms using the example of a nereid. Her body is reddish or green in color. Nereid is a predator, it feeds on organic remains and plankton.

On the head lobe of the Nereid, antennae (organs of touch), tentacles, 2 pairs of eyes and olfactory pits are noticeable. On segments of the body they have muscular outgrowths - parapodia.

Parapodia have bristles, thanks to which the worms can cling to the bottom like claws. They move either with the help of parapodia along the bottom, relying on them as levers, or they swim, bending in waves with their whole body.

The body wall of the Nereid, like other worms, is formed by a skin-muscular sac.

It consists of a single-layer epithelium covering the outside of the worm, 2 layers of muscles (annular and longitudinal) and an epithelium lining the body cavity.

Also, in each segment of the Nereid, special muscle groups are formed that control the parapodia.

body cavity Nereids secondary (general)- has an epithelial lining and is filled with fluid.

The whole is located between the organs and is an epithelial sac filled with fluid. The secondary cavity serves as a hydroskeleton (creates support during movement), carries nutrients, metabolic products, and also serves as a place for the formation of germ cells.

Cross section of the body of a Nereid

Digestive system.

Nereids develop tentacles on the head lobe, which serve to transfer prey to the mouth. The digestive system begins with the mouth, then the pharynx, equipped with chitinous outgrowths that act as teeth → esophagus → goiter → stomach → tubular midgut, hindgut → anus. The esophagus and midgut contain glands that secrete digestive juices.

Respiratory system first appears in annelids.

Most often, the respiratory organs are represented by outgrowths of the dorsal branch of the parapodia and have a branched structure. But not everyone has gills. Nereid breathes the entire surface of the body.

The internal structure of the rings on the example of an earthworm

Circulatory system also first occurs in annelids.

She is a closed type. In the circulatory system, 2 main vessels are distinguished: dorsal and abdominal. Along the entire length of the body, they are connected by transverse bridges and branch into capillaries - the smallest vessels that carry blood to all cells. Thanks to the reduction dorsal vessel(no heart) blood moves through the body of the worm.

excretory system Nereids are represented by metanephridia. They form paired excretory tubules in each segment of the body. Metanephridia consist of a funnel that bears cilia and opens as a whole.

The beating of the cilia forces the body cavity fluid into the infundibulum and then into the convoluted tubule. The tubule is densely entwined with blood capillaries, which take everything back into the blood. useful material(necessary water, vitamins and nutrients), and metabolic products and excess water are thrown out through the excretory pores.

It is characteristic that the infundibulum opens as a whole in one segment, and the excretory tubule

Metanephridia

sometimes opens outward in another segment.

Nervous system - ventral nerve cord.

It consists of the peripharyngeal nerve ring and the ventral nerve cord, which forms a ganglion in each segment (therefore, it resembles beads or a chain).

sense organs well developed in Nereids. There are organs of touch and chemical sense ("taste") - these are various outgrowths of the head lobe (antennas, tentacles, antennae). 4 eyes are well developed, there are also balance organs - statocysts.

Reproduction.

Nereids are dioecious, but their sexual dimorphism is not expressed. The sex cells of the worms are formed directly in the coelom - in females, the egg, in males - sperm. They are brought out through the channels of the excretory system. Fertilization is external - male and female gametes merge in water.

Development proceeds with metamorphosis - the trochophore larva is completely different from the adult.

She swims with the help of cilia, and after a while she settles to the bottom and turns into an adult worm.

In polychaete worms, it also occurs asexual reproduction- budding and fragmentation. Fragmentation is the division of the worm in half, after which each half restores the missing part. Sometimes a whole temporary chain of 30 worms is formed in this way.

In polychaete worms, fertilization occurs in. The value of polychaete worms. Human interaction

Habitat

Appearance and structure

Food

reproduction

Description

Habitat

Food

Enemies

reproduction

Digestive system

Circulatory system

Nervous system

excretory system

Meaning, interesting facts

Lifespan

It is interesting

Polychaete class: structure

What lifestyle do polychaete worms lead

Links:

Polychaete worms: a brief description of the class

Polychaete worms (Polychaetes)

Class Polychaeta (Polychaeta)

Polychaete class (Polychaeta) - full description.

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