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Presentation on the topic: Plate type, Sponge type

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The formation of multicellular organismsSingle-celled organisms have microscopically small sizes, and this imposes restrictions on the possibility of complication and appearance various organs for more efficient development of the habitat. The simplest way is to increase the size of the cell, but this path turns out to be a dead end - the size of the cells is limited by the ratio of surface and volume. Let's assume that a cube cell has a side length of 1 cm. Let's double the size and compare the ratios of surface areas and volumes of large and small cells.

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Formation of multicellular organisms Area of the cube: 1 x 1 x 6 = 6 cm2 Volume: 13 = 1 cm3 Ratio = 6: 1 If the face of the cube doubles in size, then the area of the cube: 2 x 2 x 6 = 24 cm2 Volume: 23 = 8 cm3 Ratio = 3: 1 Surface increased 4 times, and the volume - 8 times, which means that for each unit of surface there will now be two units of volume. It follows that with an increase in size: the cell will begin to starve, the surface will not provide nutrients to the entire volume, especially by diffusion; gas exchange becomes difficult; it becomes difficult to remove waste products; heat transfer becomes difficult.

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The formation of multicellular organisms This means that cell sizes are limited, and an increase in size is associated with the formation of multicellular organisms. How did multicellular organisms arise? E. Haeckel suggested that the volvox-shaped ancient organism, similar to the blastula, underwent a simple change. Its single-layer wall began to bulge inwards, a mouth opening and a primary intestinal cavity were formed, the outer layer of cells was ectoderm, the inner layer was endoderm. This process is called intussusception, and the resulting organism is a gastrula (from the Latin “gaster” - stomach), which has a primary digestive system. This theory is called the gastrea theory.

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The formation of multicellular organisms One of our greatest zoologists, I.I. Mechnikov, did not agree with E. Haeckel. He believed that invagination is a secondary process. I.I. Mechnikov, studying the ontogeny of lower multicellular organisms, discovered that in many of them the second layer of cells - endoderm - is formed not by invagination, but as a result of migration of amoeboid cells into the colony and, multiplying there, they form parenchyma. These cells are capable of amoeboid movement and phagocytosis. To capture large food particles, a hole appears, to which the food particles are driven using flagella. Food enters the colony and is surrounded by amoeboid cells, which form the second germ layer - the endoderm.

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Formation of multicellular organisms The remaining amoeboid cells became parenchyma, they ensure transmission nutrients to all cells of the body. Thus, the cells equipped with flagella took on the function of movement, and those that went inside the primary cavity took on the function of reproduction and nutrition. The theory of the origin of multicellular animals according to I.I. Mechnikov is called the phagocytella theory. Both points of view have their supporters, it is possible that both scientists are right and multicellular organisms were formed different ways.

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Type Lamellar (Placozoa). Since 1883, animals have been known that belong to the most primitive multicellular animals and constitute a separate phylum Lamellar (Placozoa) - Trichoplax. The dimensions of these animals are no more than 4 mm; Trichoplax is a flat plate that slowly crawls along the substrate in sea water The most surprising thing is that it does not have endoderm; it is, as it were, a blastula flattened on the surface of the substrate. The lower layer is formed by cells with flagella. It turned out that surface cells, having captured food particles, migrate to the parenchyma, where food is digested. It can be considered that in Trichoplax the endoderm is in its infancy. The discovery of Trichoplax greatly supported the theory of I.I. Mechnikov.

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Type Sponges (Spongia, or Porifera) Apart from plate animals, sponges are the simplest multicellular animals. These are sessile animals, mainly marine, do not have organs or tissues, although their various cells perform various functions. There is no nervous system, the internal cavities are lined with choanocytes - special flagellated collar cells.

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Type Sponge (Spongia, or Porifera) Almost all sponges have a complex mineral or organic skeleton. The simplest sponges have the shape of a bag, which is attached at the base to the substrate, and with the opening at the mouth) facing upward. The walls of the sac consist of two layers of cells. It is believed that the outer layer is ectoderm, the inner layer is endoderm (in fact, just the opposite).

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Type Sponge (Spongia, or Porifera) Between the layers of cells there is a structureless mass - mesoglea, in which numerous cells are located, including those that form spicules - the needles of the internal skeleton. The entire body of the sponge is penetrated by thin canals leading to the central, paragastric cavity. The continuous work of the flagella creates a flow of water through the channels into the cavity and through the mouth (osculum) out.

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Type of Sponge (Spongia, or Porifera) The sponge feeds on the food particles that water brings. This simplest type structure of sponges - ascon. But in most sponges, the mesoglea thickens and flagellar cells line the invaginations and cavities. This type of structure is called sicon, and when these cavities completely go inside the mesoglea and are connected by canals to the paragastric cavity - leukon.

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Type Sponges (Spongia, or Porifera)Sponges also usually form colonies with many mouths on the surface: in the form of crusts, plates of clods, bushes. In addition to asexual reproduction - budding, sponges also reproduce sexually. The way the larva develops is remarkable.

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Type Sponge (Spongia, or Porifera) From the egg, a blastula develops, consisting of one layer of cells, and at one pole the cells are small and with flagella, at the other - large without flagella. First, the large cells invaginate inward, then they protrude and the larva swims freely, then the flagellar cells invaginate again, which become the inner layer.

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Type of Sponge (Spongia, or Porifera) It is interesting that the larva of most sponges - parenchymula, in structure almost completely corresponds to the hypothetical phagocytella of I.I. Mechnikov. It has a superficial layer of flagellar cells, under which there are cells of an internal loose layer. It can be assumed that the phagocytella switched to a sessile lifestyle and in this way gave rise to the Sponge type.

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Type of Sponge (Spongia, or Porifera)Another feature is the amazing ability of sponges to regenerate. Even when rubbed through a sieve and turned into a pulp consisting of cells or their groups, they are capable of restoring the body. If you rub two sponges through a sieve and mix these masses, then the cells of different animals will collect into two different sponges. In nature, sponges are essential as biofilters. Settling in water bodies with significant organic pollution, they participate in their biological purification.

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Type of Sponge (Spongia, or Porifera) The practical importance of sponges is small. In some southern countries, there is a developed fishery for toilet sponges, which have a horny skeleton; freshwater sponge badyagu is used in folk medicine. Sponges have practically no enemies, except for some starfish. Others are repelled not only by the prickly skeleton, but also by the sharp, specific smell of the substances they secrete. These substances are toxic to many animals. But on the other hand, sponges in cavities and voids have many tenants and parasites - small crustaceans, worms, mollusks living under their protection.

Taxonomy
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ITIS
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Animal type lamellar(lat. Placozoa) includes only one type - Trichoplax adhaerens . They are considered the most primitive of all multicellular animals (however, as a result of reading the nuclear genome of Trichoplax, this statement has been called into question). They are not simplified descendants of sponges or coelenterates, whose mitochondrial genomes retained much less primitive features. The simplicity of Trichoplax organization is primary. These are small (about 3 mm) colorless creatures. The body shape of Trichoplax resembles a plate and is constantly changing. Several thousand cells are arranged in two layers. Between them there is a cavity filled with fluid, amoebocytes and a syncytial formation with a large number of mitochondria. There is no neural coordination. Digestion through the release of hydrolases and further phagocytosis of decomposition products. They were first discovered in seawater aquariums.

History of the study

Trichoplax was described by the German zoologist F. Schulze in 1883. In the course of his research, Schulze came to the conclusion that Trichoplax is one of the most primitive multicellular invertebrates. An unknown author tried to challenge this conclusion, stating that Trichoplax is a modified sponge parenchyma. Later, various researchers confirmed Schultz's data and recognized the primary primitiveness T. adhaerens.

Evolution and systematics

The phylum Lamelata includes the only class Trichoplacoids ( Trichoplacoidea), to which the order Trichoplacidi belongs ( Trichoplacida) with a single family Trichoplacidae ( Trichoplacidae) and two genera: Trichoplax ( Trichoplax) and Treptoplax ( Treptoplax).

Very little is known about this organism because it has never been observed in nature and has only been studied in aquarium cultures. At first, Lamellars were classified as a type Mesozoa together with Dicyemids and Orthonectids, based on the primitive structure of the organism. Later it became obvious that Lamellates are not related to other Mesozoa and cannot be attributed to them. In 1971, a separate phylum Placozoa was introduced for this species.

View Trichoplax adhaerens has been found in aquariums around the world. It is unknown whether Lamellates are cosmopolitan (distributed throughout the world).

Spreading

Trichoplax were originally found in aquariums and their life in natural habitats for a long time nothing was known.

Trichoplaxes live in the Pacific and Atlantic oceans. Nothing is known about the ecology of Lamelidae under natural conditions. Under natural conditions, these primitive animals crawl along the substrate (algae, stones, sea rocks, mollusk shells), constantly changing their body shape.

Morphology

Trichoplax is a whitish-gray translucent animal that looks like a thin plate with a diameter of up to 4 mm, irregular, variable shape, does not have anterior and posterior ends, the direction of movement is constantly changing. The outside of the body is covered with a layer of flagellar cells, which have different structure. The “dorsal” surface of the body is covered with a flat surface, and the “ventral” surface, on which the animal crawls, is covered with a high cylindrical epithelium (in relation to animals that do not have bilateral symmetry, the names “ventral” and “dorsal” surfaces are used conditionally). All these cells have a primitive feature - they lack a basal epithelial membrane.

Anatomy

Parenchyma contains fibrous cells irregular shape with long processes that connect them to one another and to the cells of the ventral and dorsal epithelium. Parenchyma cells are tetraploid, and epithelial cells are diploid. Fibrous cells contain a unique organelle not found in other organisms. It is a mitochondrial complex consisting of large mitochondria that alternate with vesicles. All together they form a kind of chain. Very small vacuoles are localized in the cytoplasm of both types of parenchyma cells. Fibrous cells, due to contractions of the cytoplasm, cause changes in the outline of the body. Their cytoplasm contains a complex system of microtubules and microfilaments that provide non-muscular contraction.

Lifestyle

They move with the help of the oscillatory movement of the cilia of the epithelium, while the shape of their body continuously changes. Eating behavior depends on the amount of food available: when the concentration of food resources is low, organisms move faster and more actively, changing shape more often. At high concentrations of food resources, they acquire a flat shape and become inactive.

Notes

Literature

Malakhov, Vladimir Vasilievich. Mysterious groups of marine invertebrates: Trichoplax, orthonectids, dicyemids, sponges. - M.: Publishing house Mosk. University, 1990. - 143 p.: ill. (DjVu)

Animal taxonomy

Sponges

Lamellar

Eumetazoans

Ctenophores · Cnidarians · Myxozoa

Bilateria

Protostomes

Shedding
Panarthropoda

Spiralia

Lophotrochozoa

Connections are not clear

Cycliophores Intraporocytic

Deuterostomes

Ambulacraria	Hemichordates Echinoderms Xenoturbellida

Single-celled organisms are microscopically small in size, and this imposes restrictions on the possibility of increasing complexity and the appearance of various organs for more efficient development of the environment. The simplest way is to increase the size of the cell, but this path turns out to be a dead end. The size of the cells is limited by the ratio of surface to volume. Let's assume that a cube cell has a side length of 1 cm. Let's double the size and compare the ratios of surface areas and volumes of large and small cells. Formation of multicellular organisms

Area of the cube: 1 x 1 x 6 = 6 cm 2 Volume: 1 3 = 1 cm 3 Ratio = 6: 1 If the face of the cube doubles, then the area of the cube: 2 x 2 x 6 = 24 cm 2 Volume: 2 3 = 8 cm 3 Ratio = 3: 1 The surface has increased 4 times, and the volume has increased 8 times, which means that for every unit of surface there will now be two units of volume. It follows that with increasing size: the cell will begin to starve, the surface will not provide the entire volume with nutrients, especially through diffusion; gas exchange becomes difficult; it becomes difficult to remove waste products; heat transfer becomes difficult. Formation of multicellular organisms

This means that the size of the cell is limited, and an increase in size is associated with the formation of multicellular organisms. How did multicellular organisms arise? E. Haeckel suggested that the volvox-shaped ancient organism, similar to the blastula, underwent a simple change. Its single-layer wall began to bulge inwards, a mouth opening and a primary intestinal cavity, an outer layer of ectoderm cells, and an inner endoderm, were formed. This process is called intussusception, and the resulting organism is a gastrula (from the Latin “gaster” stomach), which has a primary digestive system. This theory is called the gastrea theory. Formation of multicellular organisms

One of our greatest zoologists, I.I. Mechnikov, did not agree with E. Haeckel. He believed that invagination is a secondary process. I.I. Mechnikov, studying the ontogeny of lower multicellular organisms, discovered that in many of them the second layer of endoderm cells is formed not by invagination, but as a result of the migration of amoeboid cells into the colony and, multiplying there, they form parenchyma. These cells are capable of amoeboid movement and phagocytosis. To capture large food particles, a hole appears, to which the food particles are driven using flagella. Food enters the colony and is surrounded by amoeboid cells, which form the second germ layer, the endoderm. Formation of multicellular organisms

The remaining amoeboid cells have become parenchyma, they ensure the transfer of nutrients to all cells of the body. Thus, the cells equipped with flagella took on the function of movement, and those that went inside the primary cavity took on the function of reproduction and nutrition. The theory of the origin of multicellular animals according to I.I. Mechnikov is called the phagocytella theory. Both points of view have their supporters; it is possible that both scientists are right and multicellular organisms were formed in different ways. Formation of multicellular organisms

Since 1883, animals have been known that belong to the most primitive multicellular animals and constitute a separate phylum, Trichoplax (Placozoa). The dimensions of these animals are no more than 4 mm; Trichoplax is a flat plate that slowly crawls along the substrate in sea water. The most surprising thing is that it does not have endoderm; it is, as it were, a blastula flattened on the surface of the substrate. The lower layer is formed by cells with flagella. It turned out that surface cells, having captured food particles, migrate to the parenchyma, where food is digested. It can be considered that in Trichoplax the endoderm is in its infancy. The discovery of Trichoplax greatly supported the theory of I.I. Mechnikov. Type Lamellar (Placozoa).

Apart from plate animals, sponges are the simplest multicellular animals. These sessile animals, mainly marine, do not have organs or tissues, although their various cells perform different functions. There is no nervous system, the internal cavities are lined with choanocytes and special flagellated collar cells. Type of Sponge (Spongia, or Porifera)

Almost all sponges have a complex mineral or organic skeleton. The simplest sponges have the shape of a bag, which is attached at the base to the substrate, and with the opening at the mouth) facing upward. The walls of the sac consist of two layers of cells. It is believed that the outer layer is ectoderm, the inner layer is endoderm (in fact, just the opposite). Type of Sponge (Spongia, or Porifera)

Between the layers of cells there is a structureless mass of mesoglea, in which numerous cells are located, including the spines of the internal skeleton that form spicules. The entire body of the sponge is penetrated by thin canals leading to the central, paragastric cavity. The continuous work of the flagella creates a flow of water through the channels into the cavity and through the mouth (osculum) out. Type of Sponge (Spongia, or Porifera)

The sponge feeds on the food particles that water brings. This is the simplest type of structure of ascona sponges. But in most sponges, the mesoglea thickens and flagellar cells line the invaginations and cavities. This type of structure is called sicon, and when these cavities completely go inside the mesoglea and are connected by channels to the paragastric cavity leucon. Type of Sponge (Spongia, or Porifera)

Sponges also usually form colonies with many mouths on the surface: in the form of crusts, plates of clods, bushes. In addition to asexual reproduction by budding, sponges also reproduce sexually. The way the larva develops is remarkable. Type of Sponge (Spongia, or Porifera)

From the egg, a blastula develops, consisting of one layer of cells, and at one pole the cells are small and with flagella, at the other they are large without flagella. First, the large cells invaginate inward, then they protrude and the larva swims freely, then the flagellar cells invaginate again, which become the inner layer. Type of Sponge (Spongia, or Porifera)

The larva settles and turns into a young sponge (4). The peculiarities of the embryonic development of sponges give scientists reason to believe that their primary ectoderm (small flagellated cells) takes the place of endoderm. Perversion of the germinal layers occurs. On this basis, zoologists give sponges the name animals turned inside out (Enantiozoa). Type of Sponge (Spongia, or Porifera)

It is interesting that the larva of most parenchymal sponges, in structure, almost completely corresponds to the hypothetical phagocytella of I.I. Mechnikov. It has a superficial layer of flagellar cells, under which there are cells of an internal loose layer. It can be assumed that the phagocytella switched to a sessile lifestyle and in this way gave rise to the Sponge type. Type of Sponge (Spongia, or Porifera)

Another feature is the amazing ability of sponges to regenerate. Even when rubbed through a sieve and turned into a pulp consisting of cells or their groups, they are capable of restoring the body. If you rub two sponges through a sieve and mix these masses, the cells of different animals will collect into two different sponges. In nature, sponges are essential as biofilters. Settling in water bodies with significant organic pollution, they participate in their biological purification. Type of Sponge (Spongia, or Porifera)

The practical value of sponges is small. In some southern countries, there is a developed fishery for toilet sponges, which have a horny skeleton; The freshwater sponge badyagu is used in folk medicine. Sponges have practically no enemies, except for some starfish. Others are repelled not only by the prickly skeleton, but also by the sharp, specific smell of the substances they secrete. These substances are toxic to many animals. But on the other hand, sponges in their cavities and voids have many tenants and parasites of small crustaceans, worms, and mollusks living under their protection. Type of Sponge (Spongia, or Porifera) Badyaga Cup of Neptune

For the first time, representatives of the phylum Placozoa (Greek. plakos– flat; zoon- animal) was discovered by the Austrian zoologist F. Schulze back in 1883. However, until the mid-70s of the 20th century, they were considered the larva of coelenterates, until the German zoologist K. Grell discovered that Trichoplax is capable of sexual reproduction and, therefore, is an independent organism.

The lamellar ones are characterized by the following features:

1. There are no axes of symmetry; body shape can change, like amoebas.

2. There are no separate tissues or organs.

3. There is no body cavity or digestive cavity.

4. There is no nervous coordination system.

5. A body in the form of a thick plate that can move in any direction in its plane.

6. A single outer layer of flagellar cells surrounds a fluid-filled mesochyl (mesoglea), containing a network of stellate fiber cells.

7 Marine forms.

Subregnum Metazoa

Superdivisio Phagocytellozoa

Species Trichoplax reptans

Trichoplax is an irregularly shaped plate, 20 to 40 microns thick and 5-6 mm in diameter. The body consists of a single layer of flagellar cells surrounding an internal cavity in which the process (fibrous) cells are located. On the side facing the substrate (conventionally called the ventral), these cells are tall, flask-shaped, and on the opposite side (conventionally called the dorsal) they are flattened. Among the abdominal cells there are glandular cells filled with secretory vacuoles, and among the dorsal cells there are cells with large inclusions, the so-called “shiny balls”.

In the internal cavity there are fibrous cells with numerous processes that form a three-dimensional network. The processes are in contact with each other and with the cells of the ventral and dorsal layers. Actin filaments were found in the processes of these cells, thanks to which Trichoplax amoeboidally changes its shape. Fibrous cells contain large vacuoles, inside of which there are large digestive vacuoles.

Trichoplax feeds in two ways.

1 The crawling Trichoplax secretes digestive enzymes from the cells of the abdominal layer, which lyse small unicellular algae on the surface of the substrate, and then the cells of the abdominal layer phagocytose the lysis products.

2 Ingestion of whole cells by beating of bundles of cells located along the edge of the plate. This is how Trichoplax throws food onto its dorsal side. There, through the gaps between the cells of the dorsal layer, they are captured by processes of fibrous cells, and food particles end up in digestive vacuoles inside the fibrous cells.

Typically, Trichoplax reproduces asexually by fission in two or by budding “strays.” The wanderers are formed along the edge of the plate where the cells of the dorsal and ventral layers come into contact with each other. Sexual reproduction of Trichoplax is a rare phenomenon that is observed only in aging crops.

General characteristics of multicellular organisms. The process of fragmentation of an egg into many blastomere cells, from which an organism with differentiated cells and organs is formed. Haeckel's hypothesis. Structural features and biology of Placozoa. Trichoplax food.

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Llecture

animal kingdom (animalia) . Plate type (placozoa) . Sponge type (spongia)

general characteristics multicellular

All multicellular organisms have a number of specific features:

1 Possess more high level organizations than unicellular ones.

2 The body is made up of many cells that perform different bodily functions.

3 Due to specialization, multicellular cells usually lose the ability to exist independently.

4 Maintain the integrity of the body through intercellular interaction.

5 Ontogenesis is characterized by the process of fragmentation of the egg into many blastomere cells, from which an organism with differentiated cells and organs is subsequently formed.

6 Larger than unicellular organisms, which contributed to the complexity and improvement of metabolic processes, the formation of the internal environment and ensured greater stability and autonomy life processes and longer life expectancy.

Today, there are several hypotheses for the origin of multicellularity. (!) :

1 Haeckel's hypothesis. Proposed in 1874. He believed that the ancestors of multicellular organisms were spherical colonies of flagellates. He believed that the endoderm was formed by intussusception. Such an organism extinguishedTRhea.

2 Büchli's hypothesis. Proposed in 1884. According to his ideas, the ancestor was a lamellar colony of single-celled animals. By splitting the plate into two layers, a plAkula, and the gastrea is formed by bending a two-layer plate.

3 Mechnikov's hypothesis. Proposed in 1886. While studying primitive multicellular organisms, he discovered that endoderm can also be formed by immigration of cells into the cavity of the blastula. He called this layer phagocyteloblastoma, and the body itself - phageOcitella.

4 Zakhvatkin's hypothesis. Put forward in 1949. He believed that the first multicellular organisms had nothing in common with the first two hypotheses, and the phylogenetic stages did not recapitulate to the adult organisms of their ancestors, but only to free-swimming larvae. Adult individuals led an attached lifestyle and were similar to modern sponges and hydroid polyps.

5 Cellulization hypothesis, or Hadji hypothesis. He believed that multicellular organisms originated from multinucleated flagellates and ciliates, in which organelles turned into organs, and the cytoplasm became isolated near the nuclei, giving rise to new cells of one organism.

The generally accepted hypothesis today is Ivanov’s hypothesis, which is, in fact, a modified Mechnikov hypothesis.

Structural features and biologyPlacozoa

For the first time, representatives of the phylum Placozoa (Greek. plakos- flat; zoon- animal) (!) was discovered by the Austrian zoologist F. Schulze in 1883. However, until the mid-70s of the 20th century, they were considered the larva of coelenterates, until the German zoologist K. Grell discovered that Trichoplax is capable of sexual reproduction and, therefore, is an independent organism.

The lamellar ones are characterized by the following features:

1 There are no axes of symmetry; body shape can change, like amoebas.

2 No separate tissues or organs.

3 No body cavity or digestive cavity.

4 There is no nervous coordination system.

5 A body in the form of a thick plate that can move in any direction in its plane.

6 A single outer layer of flagellated cells surrounds a fluid-filled mesochyl (mesoglea), containing a network of stellate fiber cells.

7 Marine forms. (!)

Regnum Animalia (=Zoa) - Animal Kingdom

Subregnum Phagocytellozoa - Subkingdom Phagocytellozoa

Phylum Placozoa - Phylum Placozoa, or Lamellar

Species Trichoplax adhaerens

Trichoplax feeds in two ways.

Characteristics of sponges

Sponges, or porifera (lat. porus- it's time; ferre- carry) (!) - These are exclusively marine, less often freshwater, organisms. The phylum includes about 10,000 species, of which about 50 are freshwater forms. Sponges have a number of characteristic features: multicellular blastomere Trichoplax

1 There is no symmetry.

2 Multicellular with a small number of cell types; tissue organization is extremely poorly developed; organs are absent and coordination of cell functions is weak; nervous system No.

3 Choanocytes are characteristic (provide water circulation and nutrition).

4 A complex skeleton of either calcareous or silica spicules, or proteinaceous (collagen = spongin) fibers, or both types of elements may occur.

5 Cells are located around water chambers or channels varying degrees difficulties; there is no true body cavity or gut.

6 Filtration feed; gas exchange by diffusion.

7 Sessile (attached) forms only.

8 Reproduction is sexual or asexual; crushing is complete; planktonic larvae ( parenchymula And amphiblastatla).

9 Sponge cells have different functions (!) :

- pinacocytes- integumentary;

- choanocytes- water filtration and phagocytosis;

- collencytes- support;

- sclerocytes- skeleton;

- amebocytes- nutrition;

- archecites- the basis for the formation of other cells;

- myocytes- reduction;

- porocytes- form pores. (!)

The functioning of sponges is determined by one feature of their structure - the placement of cells around a system of chambers and channels through which water circulates due to the beating of the flagella of choanocytes.

There are three morphofunctional types of sponge structure: (!) ascon, sicon And lacon. The simplest asconoid organization of sponges: in the center there is a single chamber ( paragastric cavity, oratrium), surrounded by a body wall that is covered on the outside pinacocytes and riddled with pores ( ostia), allowing water to pass inside and formed porocytes, the only outlet is osculum.

This division according to body shape does not reflect the taxonomy of sponges. The most common is the leuconoid organization, which arose during the evolution of sponges through the intermediate syconoid state.

Between the flagellar chambers of sponges there is a layer of intermediate substance - mesoglea, in which lime needles lie, or spicules. Spicules can be of three types: uniaxial, triaxial and tetraaxial. (!) .

Sponges reproduce asexually, releasing small fragments of the body or clusters of cells necessary for development, mainly amoebocytes. For example, gemmules produced by freshwater sponges consist of archaeocytes covered with a durable, hard shell of spongin and spicules that allow them to overwinter. (!)(!) . Sexual reproduction often involves cross-fertilization. In this case, the sperm exits through the osculum of one individual, penetrates the pore of another, is captured by its choanocyte and transmitted to the egg.

Development to the larval stage most often occurs in the mother's body. (!) As a result of crushing, a blastula is obtained, consisting of two types of cells - small flagellated and larger granular flagellated ones. Then a two-layer embryo is formed by invagination, with large cells invaginating inside. At this point, development in the mother’s body ends, and the embryo comes out. This is where the reverse protrusion occurs. large cells, resulting in the formation of a single-layer, free-swimming larva consisting of two halves

The larva is usually a parenchymula with a solid body covered with flagella, except for one of the poles; sometimes it is a hollow amphiblastula, one of the hemispheres of which consists of small flagellar cells, and the other of macromeres without flagella. Subsequently, it leaves the parent body and for a short period of time before settling to the bottom, it leads a planktonic lifestyle.

Phylum Porifera (= Spongia) - Type of Sponge

Classis Hexactinellida (= Hyalospongiae) - Class Six-rayed, or

Glass sponges

Species Euplectella asper (! )

Representatives of this class are often called glass sponges. Their skeleton is formed by siliceous, predominantly six-rayed spicules. The body is often vase-like and about 30-40 cm tall. Syconoid forms predominate. Pinacocytes and outer integuments are a network-like syncytium formed by connected pseudopodia of amebocytes. Exclusively marine species, found mainly at great depths.

Classis Calcarea - Class Calcareous sponges

Species Sycon ciliatum (!)

Representatives of this class are distinguished by the presence of spicules made of calcium carbonate - calcite or aragonite. All three types of organization are found - asconoid, siconoid and leuconoid. The height of most species is less than 10 cm. Only marine forms.

Classis Demospongiae - Class Common sponges

Species Spongilla lacustris (!)

The largest class, uniting 90% of all known species. The skeleton consists of silica spicules and/or spongin fibers. One family (Spongiidae) includes common toilet sponges with a skeleton of only spongin. The organization is only leuconoid, some forms reach significant sizes (for example, tropical ones more than 1 m in diameter and height. The color is often shiny.

Among the representatives of this class, the so-called drilling sponges are capable of making holes in corals or mollusk shells. There are also freshwater species.

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The most common type is plate type. Topic: Lamellar type, Sponge type Objectives: To study the characteristics of the types and biology of the main representatives of each type Pimenov A.V. General characteristics of multicellular organisms. The process of splitting an egg into sets

Presentation on the topic: Plate type, Sponge type

History of the study

Evolution and systematics

Spreading

Morphology

Anatomy

Lifestyle

Notes

Links

Literature

General characteristics of multicellular organisms. The process of fragmentation of an egg into many blastomere cells, from which an organism with differentiated cells and organs is formed. Haeckel's hypothesis. Structural features and biology of Placozoa. Trichoplax food.

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