The underwater world is so diverse and unique that sometimes it is even difficult to distinguish plants from animals. Such bizarre forms are the creatures living there. Large sea giants and very microscopic planktonic crustaceans, colorful and bright, predators and herbivores - an insane variety of species of living organisms. One of these amazing creatures are sponges, which will be discussed later.

general information

You can characterize the position of these animals in the following way:

• empire - Cellular;
• kingdom - Animals;
• subkingdom - Multicellular;
• type - Sponges.

To date, it is known that there are about 8 thousand species. 300 of them inhabit the expanses of the seas of our country.

Classification

The Sponge type combines all known representatives into four large classes.

1. Calcarea, or Calcareous. Formed in the form of deposited calcium salts.
2. Ordinary, or Kremnerogovye. The main representative is a badyaga.
3. Glass (Six-beam). The class size is small.
4. Coral - a very poor species class.

All of these sponges have their own characteristics not only external, but also internal structure, lifestyle and economic importance in human life.

External structure

Perhaps the most unusual in the whole characterization of the animals in question will be precisely the external appearance. The features of the external structure of the sponge are determined by the variety of body shapes that are characteristic of them. So, representatives of different classes can be in the form:

• glasses;
• bowls;
• tree structure.

The symmetry of the body in single forms is bipolar axial, in colonial forms it is mixed. Each individual has a special flat sole, with which it is attached to the bottom or other substrate. Sponges lead most often an immobile way of life.

On the upper side of the body is a special opening, which is called the "osculum". It serves to remove excess water from the internal cavity. Outside, the body is covered with a layer of cells - pinacoderm. They resemble in their structure the epithelial tissue of higher animals.

However, they also have distinctive features - the presence of wide pores. The structure of the sponge provides for the absorption of food particles not through the upper hole, but through numerous perforations penetrating the entire body, capable of contracting and expanding.

Under the outer layer are two more, which we will consider in more detail later. The color scheme of both single and colonial forms is quite diverse. There are the following types of coloring:

• gray;
• green;
• purple;
• yellow;
• white;
• red;
• brown;
• mixed.

The Sponge type brings the underwater world to life, making it even brighter, more colorful and attractive. Moreover, if we consider a single individual on the land surface, then it will have a very unattractive appearance: a brownish slippery lump resembling a raw liver, emitting a not very pleasant aroma.

The internal structure of representatives

Sponge body types are similar, whether solitary or attached to a colony. Immediately under the dermal outer layer of porous cells is a special intercellular substance that forms a fairly voluminous membrane. In it, the cells are located loosely, and their shape is different. The tissue is somewhat reminiscent of fatty tissue in higher terrestrial representatives. This structure is called mesohyl.

Under this layer is an internal cavity lined with a special row of cells. This is the gastric layer. All food goes here, and digestion takes place here. All waste products, together with excess water, are sent to the upper opening of the body and are removed through it to the outside.

Also, the structure of the sponge necessarily includes a kind of skeleton. It is formed from lime, phosphorus, organic salts, which are produced in special mesochil cells. It not only gives the sponges a certain shape of the body, but is also important for the preservation of the internal cavity from mechanical damage.

The characteristic of the Sponge type will be incomplete if the main feature of these animals is not indicated - their body does not have tissues, but only includes layers of various shapes and forms. This is the main difference between the considered animals from all others.

The aquifer system of individuals is also interesting. It may be different for different classes. There are three main types of it:

1. Ascon - all communication with the external environment is carried out through a system of tubes through which water moves into special cell-chambers. The most simplified aquifer system found in a few representatives.
2. Seacon. A more advanced system, which includes a network of branched tubules and tubules that flow into special cell-cameras with flagella.
3. Leikon - a whole network of osculums, this type of aquifer system is typical only for colonial forms. The most complicated option against the background of all the previous ones.

Sponges reproduce both sexually and asexually. Sex cells are formed in the mesohyl layer. Then the products go out through the pores of the body and with the flow of water enter the bodies of other sponges, where fertilization occurs. As a result, a zygote is formed, giving rise to a larva. The fry can be called differently: amphiblastula, parenchymula, celloblastula.

If we talk about that, it is based on the process of budding, that is, detachment with subsequent regeneration of the missing structures. For the most part, the Sponge type includes hermaphroditic animals.

Lifestyle features

If we consider the whole variety of multicellular animals of the world, then sponges should be attributed to the most primitive stage in terms of organization. However, these are also the most ancient animals that appeared many thousands of years ago. During the evolution of their organization, little has changed, they retain their characteristics over time. The life form of representatives has two manifestations:

• single;
• colonial.

Most often, mass accumulations of sponges are found among coral reefs. There are both freshwater species (their minority) and oceans (the overwhelming majority of species).

The Sponge type includes animals that feed on small organisms or their remains. In the structure of their body there are special collar cells with flagella. They just capture the floating particles of food, directing them into the internal paragastric cavity of the body. Digestion takes place inside the cells.

According to the method of obtaining food, sponges can be called passive hunters. They sit lazily in an attached place, waiting for passing nutrient particles. And only when they are already very close, they capture them through the pores and direct them, together with the flow of water, into the body.

Some species are able to move, despite the fact that they still have soles for attaching to the substrate. However, their speed is so low that for the whole day the individual is unlikely to move further than a meter.

Variety of sponges

For such primitive representatives, it is quite impressive - after all, there are about 8 thousand species of them! And according to some modern data, this figure is already approaching 9 thousand. External diversity is explained by the difference in body shape, skeleton types and body color of individuals (or colonies).

Grade Glass Sponges

Glass sponges are very interesting in their external variety. They are not as numerous as others, but have an unusual skeleton. These are one of the largest individuals that the Sponge type includes. The general characteristics of the representatives of this class can be expressed in several points.

1. The Latin name of the class is Hexactinellida.
2. The skeleton is formed from silicon compounds, so it is very durable.
3. Needle type body support, which is dominated by six-pointed structures.
4. Larvae of parenchymula or coeloblastula species.
5. Aquifer system of the leukon type.
6. More often colonial than solitary forms.
7. Sometimes up to 50 cm in height.

The most common representatives are such as:

• hyalonema siboldi;
• euplectella.

Class Ordinary, or Kremnerogovye, sponges

The Sponge type, a photo of whose representatives can be seen in this article, also includes the most numerous class in terms of the number of individuals - Kremnerogye, or Ordinary. They got their name for the features in the structure of the skeleton - it consists of silica and spongin. The hardness is quite gentle and easily destroyed. The shape of the spines of the skeleton is very diverse:

• asterisks;
• anchors;
• clubs;
• sharp needles and so on.

The most common freshwater representative is badyaga - a sponge used as an indicator of the purity of the reservoir. Outwardly unattractive, the color is brown-brown, sometimes dirty yellow. Used by man for various needs.

What other representatives are found among ordinary sponges?

1. Mixils.
2. Sea caravan.
3. Baikal sponge.
4. Marine brushes.
5. Giant chondrocladia and others.

Class Lime sponges

It includes representatives with a strong and beautiful calcareous skeleton. They live only in the seas and oceans. The coloration is pale or completely absent. The spines of the skeleton may have about three rays. The main representatives: ascons, sicons, leukandry.

Class Coral sponges

The fewest representatives that outwardly resemble coral branches. This happens due to the formation of a powerful calcareous skeleton of different colors and patterned structure.

Representatives: Nicholson's geratoporella, merlia. In total, only six species of such animals have been described. For a long time they were not distinguished from the coral reef system, so they were discovered relatively recently.

Human use of sponges

The economic importance of individuals belonging to the Sponge type is also important. Representatives are used for the following purposes:

1. They are participants in the food chain, as they themselves serve as food for many animals.
2. Used by people to make beautiful jewelry for the body and home interior.
3. They contain substances that allow them to be used for medical purposes (the bodyaga sponge has a resolving bruises and wound healing effect).
4. They are used to create hygienic sponges - natural natural products for the cosmetic industry.
5. Used for technical and other purposes.

Sponge type (Porifera, from Latin porus - it's time, ferre - to carry). This type includes primitive multicellular animals leading a sedentary lifestyle, attached to solid substrates in water. Approximately 5,000 species are known, most of them marine.

The body is radially symmetrical and, in principle, consists of a central (paragastric) cavity surrounded by a two-layer wall. Water enters through the pores in the wall into this cavity, and from there it goes out through a wide mouth - at its upper end; however, in some sponges, the mouth is reduced or absent, which leads to an increase in the flow of water through the pores. Its movement is due to the beating of the flagella, which are supplied with cells lining the channels in the walls. Food, oxygen, sex products and waste products of metabolism are carried by this almost external water.

Appearance

The appearance of the sponge is very characteristic. In addition to the branched form, Baikal sponges can be crusty, spherical, mushroom-shaped (the type of Svarchevskaya papiration has the form of small whitish graceful “caps”, 1-4 cm in diameter). The sizes of sponges vary widely: from 1-2 cm in diameter in flat forms and up to 1 m in height in tree-like ones. All Baikal sponges are stronger and tougher than badyagi. The tissue of the sponge is very dense and elastic, it is torn with some effort. All sponges, both freshwater and marine, are characterized by a peculiar pungent and unpleasant odor.

Almost all freshwater sponges grown in the light are bright green in color. It depends on the symbiotic unicellular zoochlorella algae that live in their body. Sponges grown at depth or in the shade do not have a green color. Such sponges can be off-white, brown, bluish or reddish in color. Sometimes only part of the colony is green. Various species growing in the coastal zone of Lake Baikal differ in shades of green.

Internal structure of sponges

Examining the sponge, cutting it, we do not find in it any organs visible to the naked eye, but we see only a rough to the touch substance, riddled with voids and channels. When studying a sponge under a microscope at low magnifications, two elements can be distinguished in it: the skeleton and the parenchyma. The skeleton consists of silicon needles or spicules glued together in bundles with a transparent substance - spongin. The bundles of spicules form a more or less regular network or spatial lattice in the body of the sponge. The shape of the spicules and the architectonics of the skeleton, i.e. the location of the spicule bundles are of diagnostic value and are characteristic of each species. Spicules with rounded ends are called strongyls, spicules with pointed ends are called oxi. Unlike badyags, Baikal sponges have a very strong skeleton, because their spicules are soldered with a large amount of spongin.

The skeleton penetrates the soft mucous substance - the parenchyma and serves as its support. The parenchyma consists of mesoglea and cellular elements scattered in it, for which mesoglea plays the same role as blood plasma for blood cells. The sponge contains several types of cells. Outside, the sponge is covered with dermal cells. The internal cavities, the so-called flagellar chambers, are lined with choanocytes that have a constantly moving long cord. Silicoblasts and spongioblasts are involved in the formation of silicon spicules. Amebocytes are located in the mesoglea and have the potential to produce all other cellular elements, including the gonads. Nerve cells in sponges are absent, respectively, there is no irritability.

The cavities that permeate the entire body of the sponge form the most important, so-called irrigation system, which is divided into two parts - the inlet and outlet. The adductor system begins with numerous pores on the surface of the sponge and branches into adductor channels and cavities. The channels of the efferent system, gradually merging with each other into larger ducts, also approach the surface of the sponge and flow into the ocular openings or osculums. Thin walls everywhere separate the inlet system of channels from the outlet system similar to it, and nowhere is there a direct connection between them. Such communication occurs only in the flagellar chambers.

The movement of the cords in the flagellar chambers represents the engine that creates a continuous flow of water through the entire body of the sponge. The harnesses make constant helical movements. Thus, each of the countless chambers acts as a pump. Their combined efforts cause water to enter the pores, pass through the entire complex system of channels and be ejected through the ocular holes.

The vital activity of sponges

The sedentary lifestyle of sponges makes them look like plants. However, some of their cellular elements have amazing mobility. The speed of movement of some cells varies from 0.6 to 3.5 microns per minute (1 micron \u003d 1/1000 mm - approx. site). If a piece of a living sponge is rubbed through a fine sieve and a few drops of such pomace are stirred in a small amount of water, then under a microscope one can see a mass of living cells that move, releasing pseudopodia. Silicoblasts, which take part in the construction of silicon spicules, which are formed inside the mother cell, are especially mobile.

First, an axial filament appears, to which silicoblasts approach and deposit layers of silica on its surface until the spicule reaches the required thickness. The finished spicule is then moved into the mesoglea by other cells, which put it in its proper place in the skeletal bundle. Gluing it to the bundle is the task of spongioblasts that secrete spongin.

Sponges feed on particles suspended in water. Water, passing through the pores, enters the flagellar chambers, where small particles are captured by choanocytes, and then thrown into the mesoglea, where they are reabsorbed by other cells - amoebocytes, which digest them and carry nutrients throughout the body. Sponges lack selectivity and capture both nutrients and non-nutrients. The sponge is gradually freed from inedible particles, removing them through the osculums. Thus, substances suspended in water serve as food for sponges, if the size of the particles allows them to pass through the pores. But the amount of suspended solid food is not enough to feed sponges, and organic substances dissolved in water are an additional source. Along with the flow of water, oxygen enters the body of the sponge.

Sponge breeding

All sponges are dioecious. Some individuals produce only eggs, others spermatozoa, although outwardly male and female individuals do not differ in any way. Spermatozoa penetrate through the pores along with the water current inside the females and fertilize the eggs. The formation of the larva takes place inside the mother's body. When the larva matures, it leaves it and becomes free-swimming for a while. Rotating, the larva swims briskly in search of a suitable substrate.

Attachment of the larva usually occurs within the first 12 hours after leaving the mother's body, but sometimes it can be delayed up to two days. The settled larva flattens out, turning into a small whitish spot, in which very soon you can recognize a small sponge. During the development of a sponge from an egg to a free-swimming larva, there is a complete resemblance to the embryonic development of other animals. But the metamorphosis of the larva, which begins after its attachment, is a process characteristic of all sponges, which distinguishes them from all other multicellular animals. The germ layers change places, for this reason sponges are called animals "turned inside out".

All freshwater sponges, except Baikal, also have a process of asexual reproduction, the result of which is the formation of gemmules. These are dormant stages designed to preserve the species during unfavorable seasons (cold or dry). Spongyllid gemmules also perform the function of settling in other water bodies, where they can be brought by wind, water birds, or in another way. Gemmules remain viable for several years, are able to tolerate freezing and drying out.

A very important difference between endemic Baikal sponges and cosmopolitan spongyllids is their lack of ability to reproduce with the formation of gemmules. The constancy of the temperature regime of the deep-water lake contributed to the disappearance of this stage from their development cycle. Interestingly, some cosmopolitan spongyllids living in Baikal have also lost the ability to form gemmules.

The biological significance of sponges

Being active biofilter feeders and due to their mass distribution in Baikal, sponges form an important link in the lake's ecosystem and play a significant role in its hydrobiological regime. The role of sponges is determined by their participation in trophic chains, since they are the most important consumers of zoo- and phytoplankton that develop in the thickness of coastal waters, as well as silicon necessary for the construction of the skeleton.

Ecology and practical importance of sponges

Sponges reach the greatest species diversity in the tropical and subtropical zones of the World Ocean, although there are many of them in arctic and subarctic waters. Most sponges are inhabitants of shallow depths (up to 500 m). The number of deep-sea sponges is small, although they were found at the bottom of the deepest abyssal depressions (up to 11 km). Sponges settle mainly on stony soils, which is associated with the way they feed. A large number of
silt particles clog the channel system of the sponges and make their existence impossible. Only a few species live on muddy soils. In these cases, have
they usually have one or more giant spicules that stick into the silt and raise the sponge above its surface (for example, species of genera
Hyalostylus from Hyalonema). Sponges that live in the intertidal zone (on the littoral), where they are exposed to the action of the surf, look like growths,
pads, crusts, etc. In most deep-sea sponges, the skeleton is flint - strong, but fragile, in shallow-water sponges - massive or elastic
(horny lips). By filtering huge amounts of water through the body, sponges are powerful biofilters. By this they contribute to the purification of water from mechanical and organic pollution.

Sponges often cohabit with other organisms, and in some cases this cohabitation has the character of simple commensalism (lodging), in others it takes on the character of a mutually beneficial symbiosis. So, the colonies of sea sponges serve as a place for the settlement of a large number of different organisms - annelids, crustaceans, serpentine (echinoderms), etc. In turn, sponges often settle on other, including mobile, animals, for example, on the shell of crabs, gastropod shells etc. Some, especially freshwater sponges, are characterized by intracellular symbiosis with unicellular green algae (zoochlorella), which serve as an additional source of oxygen. With excessive development, algae are partially digested by sponge cells.

Drilling sponges (genus Cliona) represent a peculiar ecological group. Settling on a calcareous substrate (mollusk shells, coral colonies,
calcareous rocks, etc.), they form passages in it that open outwards with small holes. Outgrowths of the body of the sponge protrude through these openings,
bearing osculums. The mechanism of action of drilling sponges on the substrate is still unclear. In the dissolution of lime, apparently, an essential role is played by the carbon dioxide released by the sponge.

The practical value of sponges is small. In the southern countries there is a trade of toilet sponges with a horn skeleton, used for washing and various technical purposes. They are caught in the Mediterranean and Red Seas, the Gulf of Mexico, the Caribbean Sea, the Indian Ocean, off the coast of Australia.
There is also a fishery for glass sponges (mainly Eupectella) used as jewelry and souvenirs off the coast of Japan.

Classification

Sponge type classification is based on the composition and structure of the skeleton. There are three classes.

Class I. Lime sponges (Calcarea, or Calcispongia)

The skeleton is composed of carbonic lime needles, which can be four-, three-, or one-axle. Exclusively marine, mostly shallow-water small sponges. They can be built according to the asconoid, syconoid or leuconoid type. Typical representatives are the genera Leusolenia, Sycon‚ Leuconia.

Class II. Glass sponges (Hyalospongia)

Marine mainly deep-sea sponges up to 50 cm high. The body is tubular, bag-shaped, sometimes in the form of a glass. Almost exclusively solitary forms of the syconoid type. The flint needles that make up the skeleton are extremely diverse, triaxial at the base. Often soldered at the ends, forming lattices of varying complexity. A characteristic feature of glass sponges is the weak development of mesoglea and the fusion of cellular elements into syncytial structures. Typical genus Euplectella. In some species of this genus, the body is cylindrical, up to 1 m in height; the needles at the base, sticking into the ground, reach 3 m in length.

Class III. Ordinary sponges (Demospongia)

Most modern sponges belong to this class. The skeleton is flint, spongy, or a combination of both. This includes a detachment of four-beam sponges (Tetraxonia), the skeleton of which is composed of four-axis needles with an admixture of uniaxial ones. Characteristic representatives: spherical large geodia (Geodia), brightly colored orange-red sea oranges (Tethya), lumpy bright cork sponges (family Suberitidae), boring sponges (family Clionidae) and many others. The second detachment of the Demospongia class is the silicon-horned sponges (Cornacuspongia). The skeleton includes spongin as the only component of the skeleton or in various proportions with flint needles. This includes toilet sponges, a few representatives of freshwater sponges - badyag from the family. Spongillidae, endemic Baikal sponges of the family. Lubomirskiidae.

Sponge type, the structural features of which we will consider in our article, are still a mystery of nature to this day. And in textbooks on zoology, there is not so much information about them. But sponges are a type of multicellular animals and are widespread in nature.

Subkingdom Multicellular

Over time, as a result of evolutionary transformations, along with the simplest in nature, multicellular animals also appeared. They have a number of more complex structural features. And the point is not only in the number of cells, but in their specialization to perform various functions. Some of them serve for reproduction, others provide movement, and still others - the processes of splitting substances, etc.

Groups of cells, identical in structure and function, are combined into tissues, and they, in turn, form organs.

Sponge type: general characteristics

Sponges are the most primitive multicellular animals. They do not yet form true tissues, but cells are distinguished by strict specialization.

Sponges are ancient animals. Some of their species have been known since the Precambrian and Devonian periods. Scientists consider calcareous flagellates to be their ancestors. But the branch of evolution of sponges turned out to be a dead end.

For a long time, taxonomists could not determine their position in the system of the organic world. Therefore, sponges were called zoophytes - organisms that have signs of both animals and plants. Everything changed only at the beginning of the 19th century. Sponges were finally assigned to the animal kingdom. But scientists are still arguing: whether these are colonies of protozoa, or real multicellular organisms.

Basics of classification

According to the types of structure of sponges, they are combined into several classes:

• Ordinary. Among them there are solitary and colonial forms. They look like growths, plates, lumps, small bushes, the height of which can reach half a meter. Representatives of this class are badyagi, toilet and drilling sponges.
• Lime. They are characterized by the presence of an internal skeleton, the needles of which are composed of calcium carbonate. The shape of the body is in the form of a barrel or tube. Representatives are sicon, ascetta, leucandra.
• Coral. Exclusively colonial forms. The internal skeleton is composed of calcite or silicon. The size of the colonies in width reaches a meter. They got their name due to the fact that they live among the coral reefs of the Indian and Pacific Oceans.
• Glass, or Six-beam. Solitary goblet-shaped specimens. They have a skeleton made of silicon in the form of needles. They live exclusively in ocean waters. Due to their aesthetic appearance, they are used for making jewelry.

Structural features

Most representatives of the Sponge type have a goblet body. With its base, the animal is attached to the substrate - stones, the bottom of reservoirs or shells. The upper part opens outwards with a hole leading into the body cavity. It's called atrial.

All Sponge-type classes are two-layered animals. Outside is the ectoderm. This layer is formed by squamous cells of the covering epithelium. The inner endoderm is made up of flagellar cells called choanocytes.

The walls are not continuous, but penetrated by a large number of pores. Through them, the exchange of substances of sponges with the environment occurs. Between the layers of the body is a gelatinous substance - mesoglea. It contains three types of cells. These are the supporting ones that form the skeleton, sexual and amoeboid. With the help of the latter, the process of digestion is carried out. They also ensure the regeneration of sponges, since they can turn into any type of cell.

The size of the sponges varies from 1 cm to 2 m, and the color is from cloudy brown to bright purple. The shape of the body is also different. Sponges can look like a plate, a ball, a fan or a vase.

Food

According to the method of feeding, representatives of the Sponge type are heterotrophic filter feeders. Water constantly moves through their body cavity. Thanks to the activity of flagellar cells, it enters the pores of the layers of the body, enters the atrial cavity and exits through the mouth.

At the same time, protozoa, bacteria, phytoplankton and the remains of dead organisms are captured by amoebocytes. This happens by phagocytosis - intracellular digestion. Unprocessed food remnants again enter the cavity and are thrown out through the mouth.

Among the sponges there are also predators. They do not have an aquifer filtration system. They feed on small crustaceans and fish fry, which stick to their sticky threads. Then they shorten, pulling themselves up to the body of the predator. The sponge wraps around the prey and digests it.

Respiration and excretion

Animals belonging to the Sponge type are not found on land. Therefore, they are adapted to absorb oxygen only from water. This happens with the help of diffusion. All cells of the body of sponges are capable of absorbing oxygen, as well as removing carbon dioxide.

asexual reproduction

Despite the primitiveness of the structure, the methods of reproduction of sponges are quite diverse. They can reproduce by budding. In this case, a protrusion appears on the body of the animal, which increases in size over time. When all types of cells have formed on such a kidney, it detaches from the maternal individual and proceeds to an independent existence.

The next way sponges reproduce is fragmentation. As a result, the body of the sponge is divided into parts, each of which gives rise to a new organism. This process is also called gemmulogenesis. It usually occurs with the onset of adverse conditions.

The resulting parts of the sponges are called gemmules. Each of them is covered with a protective shell, and inside contains a supply of nutrients. Gemmules are considered to be the resting stages of sponges. Their ability to survive is simply incredible. They remain viable after exposure to low temperatures down to -100 degrees and prolonged dehydration.

sexual reproduction

The sexual process is carried out by specialized cells. In this case, the spermatozoon leaves the mouth of one sponge and enters the other with a stream of water. There, amoebocytes deliver it to the egg.

According to the type of development among the sponges, oviparous and viviparous are distinguished. In the former, the division of the fertilized egg and the formation of the larva occurs outside the maternal organism. Such organisms are always dioecious. Among viviparous representatives, hermaphrodites are often found. In them, the development of the zygote is carried out in the atrial cavity.

Ecology

For the distribution of Sponge-type animals, the presence of a certain substrate is of great importance. It must be solid, as silt can clog into the pores. This leads to mass death of animals.

A characterization of the Sponge type would be incomplete without mention of symbiosis. In nature, cases of their mutually beneficial cohabitation with other aquatic inhabitants are known. It can be algae, bacteria or fungi.

With this form of existence, the metabolism of sponges occurs more intensively. For example, when cohabiting with algae, they release several times more oxygen and organic matter. Since adult sponges are inedible, many animals use them to protect themselves from enemies. There are cases when crustaceans settle in them. And crabs prefer to wear sponges on their shells.

Significance in nature and human life

Sponges are of great importance for cleaning water bodies. By filtering, they not only feed, but also remove impurities. These animals also play their role in food chains. Sponge larvae feed on mollusks and certain types of fish.

For humans, sponges are raw materials for pharmacology. Everyone knows ointments for bruises and bruises based on sponges - badyagi, as well as iodine-containing drugs. The meaning of these animals is also associated with their name. They have been used for a really long time for washing the body and various surfaces. And now we call such synthetic products sponges.

So, in the article we examined the representatives of the sub-kingdom Multicellular - the type of Sponge. These are multicellular aquatic animals that lead an attached lifestyle. In their body, two layers are distinguished - ecto- and endoderm. Each of them is formed by specialized cells. Sponges do not form true tissues.

Sponges are multicellular aquatic, mainly marine, animals that are motionlessly attached to the bottom and underwater objects. Symmetry is absent or there is indistinct radial symmetry. Organs and tissues are not expressed. The internal cavities are lined with choanocytes - special flagellar collar cells. The nervous system is missing. The body is permeated with numerous pores and channels extending from them, communicating with cavities lined with choanocytes. Through the body of the sponge is a continuous flow of water. Almost all have complex mineral or organic skeletons.

Sponges are in the form of a deep glass, which is attached to the substrate with its base, and faces up with a hole. In addition to this, the openings of the sponge wall are permeated with the thinnest pores leading from the outside to the internal, paragastric cavity.

The body consists of two layers of cells: outer - dermal (ectoderm) and inner, lining the internal cavity - gastric (endoderm). Between them, mesoglea stands out - a layer of a special structureless substance with individual cells scattered in it. In most sponges, the mesoglea is strongly thickened. The skeleton is also formed in the mesoglea. The outer layer of sponge cells is in the form of a squamous epithelium. The smallest pore tubules passing through the walls of the body of the sponge open outward, penetrating individual cells of the outer layer (porocytes). The gastric layer is composed of special collar cells (choanocytes). They have a cylindrical shape, and from the center of the free end of the cell protruding into the paragastric cavity, a long flagellum protrudes, the base of which is surrounded by a cytoplasmic collar.

The simplest form of sponge structure is called the ascon type. However, in most species, this stage is transient and is characteristic only for young individuals.

The number of flagellar chambers in sponges is large. A variety of cellular elements are scattered in the mesoglea. There is a significant number of immobile stellate cells, which are connective tissue supporting elements (collencytes). The second category is scleroblasts - cells inside which individual skeletal elements of sponges are laid and develop. In addition, a significant number of motile amoebocyte cells is located in the mesoglea. Among the latter, one can distinguish the cells inside which the digestion of food received from choanocytes takes place. Some amoebocytes - archeocytes are undifferentiated reserve cells that can turn into all of the listed cell types, as well as give rise to germ cells. Thus, endoderm choanocytes can lose their bundles and go into the mesoglea, turning into amoebocytes. In turn, amoebocytes turn into choanocytes. Integumentary (ectodermal) cells can also go deep into the mesoglea, giving rise to amoeboid cells. In some groups, a secondary fusion of almost all cellular elements occurs, which leads to the formation of syncytia.

It is generally accepted that sponges have no nervous system at all. But in the mesoglea, special stellate cells are described, interconnected by processes and giving processes to the ectoderm and flagellar chambers. These cells are considered as nerve elements that transmit irritation

Skeleton

Only in a few sponges the body remains completely soft, in the majority the skeleton is solid and serves to support the body and the walls of the canal system.

The skeleton consists either of a mineral substance: carbonic lime or silica, or of the organic substance of spongin, resembling horn in its properties, or of a combination of silica and spongin. The skeleton is always placed in the mesoglea.

The mineral skeleton consists of microscopic bodies, needles (spicules) that form inside special skeletal-forming cells, or scleroblasts. A small grain appears in the cytoplasm of the scleroblast, which increases, grows and forms a regular skeletal needle. During growth, the needle is surrounded by scleroblast cytoplasm, which covers the needle with the thinnest layer. Growth occurs by deposition on the surface of the needle of new layers of mineral matter. When the needle reaches its maximum size, its growth stops, the scleroblast dies off and the needle remains free to lie in the mesoglea.

The needles are usually of regular geometric shape and varied, but can be grouped into four main types: uniaxial, two, three, four.

The horny, or spongy, skeleton consists of a network of yellowish horny fibers strongly branching inside the mesoglea. The chemical backwardness of spongin is close to silk, moreover, with some, sometimes quite significant, content of iodine.

there are sponges completely devoid of a skeleton. The non-skeletal sponges are very small - evidence of the reference value of the skeleton, without which the sponges cannot grow.

Reproduction and development

Sponges reproduce asexually and sexually. Asexual reproduction is by budding. A tubercle appears on the surface of the sponge, into which all layers of the body and the paragastric cavity continue. This tubercle gradually grows, at the end of which a new osculum breaks through.

Complete separation of the kidney occurs relatively rarely, usually the daughter individuals remain in contact with the mother - a colony appears. The boundaries between individual individuals can be smoothed out, so that the entire colony merges into a common mass. In such colonies, the number of merged individuals can be judged from the number of osculums.

A special method of internal budding exists in the freshwater sponge badyagi. In summer, badyaga reproduces by ordinary budding and sexually. But by autumn, in the mesoglea of ​​the badyagi, the formation of special spherical clusters - gemmules - by amoeboid cells is observed. A gemmula is a multicellular mass surrounded by a shell of two horny layers, between which there is a layer of air with small silica needles set perpendicular to the surface of the gemmule. In winter, the badyagi's body dies and disintegrates, and the gemmules fall to the bottom and, protected by their shell, remain until the next spring. Then the cell mass contained inside the gemmul crawls out, attaches to the bottom. and develops into a new sponge.

Most sponges are hermaphrodites, some species have separate sexes. Their sex cells originate from amoeboid cells (archaeocytes) crawling in the mesoglea. They lie in the mesoglea under the endoderm of the flagellar chambers. The gums enter the cavity of the canal system, are excreted through the osculum, penetrate into other sponges that have mature eggs, and fertilize the latter. The initial stages of egg development take place inside the mother's body. In some calcareous sponges, development proceeds as follows. The egg for the most part experiences complete and at first uniform crushing, giving successively the beginning of 8 blastomeres, lying like a corolla in the same plane. Further, the embryo is divided by the equatorial groove into 8 small upper and 8 larger lower cells. With further development, small blastomeres divide faster than large ones. It turns out blastula , in which the upper half consists of small cylindrical micromere cells equipped with flagella, and the lower half consists of large granular macromeres. Due to the difference in blastomeres at the poles, the sponge blastula is called amphiblastula. The amphiblastula undergoes a peculiar change. Its large-celled half begins to bulge into the small-celled, but the process soon stops , large cells protrude back and the larva returns to the state of amphiblastula.The latter exits the body of the sponge through a system of channels and after a while the larva is attached to the substrate by the pole on which small, flagella-bearing cells are located. it is two-layer. The larger amphiblastula cells form the outer layer.

In sponges, the blastula poles protrude twice into unknown sponges and some calcareous sponges have a different embryonic development. In many of them, as a result of crushing, a blastula is formed, the walls of which consist of more or less identical cells equipped with flagella. Subsequently, individual cells of the blastula wall crawl into its cavity, which is gradually filled with loosely located cellular elements. At this stage, the larva is called parenchymula. Subsequently, the parenchymula sinks to the bottom, its superficial flagellar cells sink inward and give rise to the collar epithelium. The cells of the inner layer, on the contrary, come to the surface and form the integumentary cell layer and mesoglea of ​​the sponge. Thus, perversion of the germ layers also occurs in this type of development. .

Sponges are very peculiar animals, so researchers have been deciding for a long time whether these organisms should be attributed to plants or animals. About 4500 species of sponges are known. All of them, with the exception of a small number of freshwater ones, live in the seas and oceans. Sponges are the most primitive multicellular organisms.

The body shape of the sponges resembles a glass or a bag (Fig. 1). These are sessile solitary or more often colonial forms. The entire body of a sponge is riddled with pores. Through them, water with dissolved oxygen and floating small organisms penetrates into the sponge, which the sponge uses as food. Water comes out of the sponge through the outlet - the mouth (osculum).

The outer layer of the body (ectoderm) consists of flat surface cells. The inner layer (endoderm) is built from flagellated collar cells (choanocytes), similar to colonial flagellar cells. Choanocytes capture food, which is then digested inside the cells. In addition, special mobile amoeboid cells also capture food and digest it. Consequently, sponges have intracellular digestion, there is no digestive system yet. Between the outer and inner layers of cells is the gelatinous substance of the mesoglea. Cells of different function are scattered in it: amoeboid cells, which serve for digestion, mature and immature gametes, skeletoblasts, i.e., forming a skeleton. The skeleton is built from the organic matter of spongin or from one-, three-, and four-axis calcareous and flint needles (spicules), also located in the mesoglea.

Sponges reproduce asexually (by budding) and sexually. They have a well-defined ability to regenerate.

With the development of sponges, a peculiar process occurs. The outer layer of flagellar cells that form in larvae subsequently turns into the endoderm (and not into the ectoderm, as in other animals), and the inner layer of embryonic cells, usually giving endoderm, into the outer cells of an adult animal. In no other type of multicellular animals, except for sponges, such a phenomenon is observed.

It can be seen from the above description that, unlike protozoa, in which all vital functions are performed by one cell, the sponge has a division of functions between cells and the associated morphological differentiation. But there are still no or almost no connections between cells, no coordination of functions.

There are two points of view regarding the origin of sponges. The presence of collar cells in sponges gives reason to assume their origin from some ancient colonial collar flagellates, independently of the rest of the animal world. However, their origin is more likely from the hypothetical ancestor of all multicellular organisms - phagocytella, with which the larva found in most sponges, the parenchymula, is very similar in structure. The progressive development of sponges due to a sedentary lifestyle has stopped, and their structure may have been simplified. The development and structure show that sponges stand apart from other types of multicellular organisms and in phylogenetic terms represent a blind branch of the family tree of animals.

The practical value of sponges is small. A number of sea sponges, called toilet sponges, have been mined from the bottom of the sea since ancient times and, after drying, are used for washing. In our fresh waters there is a bodyaga sponge that forms growths on underwater objects. It is used in folk medicine as an external antirheumatic agent.