Belongs to the type of echinoderm, an invertebrate animal. Otherwise called sea cucumber or sea capsule. Among them there are also edible species called “trepang”.

Holothuria includes a huge number of species, more than 1100 species, all species are divided into 6 orders. The difference between the orders lies in the variety of tentacle shapes and the different presentation of the calcareous ring. The structure of internal organs also differs among representatives of different orders.

Only 100 species are common in Russia. Findings of fossils of all kinds of holothurians are related to the Silurian period (the third period of the Paleozoic, following the Ordovician).

Biological facts about sea cucumbers

How do holothurians differ from other echinoderms?

Basically, the peculiarity of holothurians is the presence of an elongated, worm-like, oblong body shape; a spherical shape is less common.

Also, holothurians do not have spines, they have a reduced dermal skeleton, it consists of small calcareous bones. They have a pentaradial symmetry of the body, and many organs are located bilaterally.

The skin of these sea cucumbers is rough to the touch, with numerous wrinkles. The body has a dense wall with high turgor (density). The muscle bundles are highly developed. The esophagus is surrounded by longitudinal muscles; they are attached to a calcareous ring. One end of the body is represented by the mouth, and the other end has the anus. The mouth around is crowned with tentacles, their function is to capture food and transfer it to the intestines, which are twisted into a spiral.

For breathing, sea cucumbers have a special ambulacral (hydraulic) system, as well as aquatic lungs. They are represented by bags that open in front of the anus into the cloaca.

Sea cucumbers lie on the bottom, on their sides, which is not a characteristic feature of other echinoderms. The ventral side is represented by three rows of ambulacral legs, and the dorsal side consists of two rows of such legs. The ventral side is called trivium, and the dorsal side is called bivium. Some sea cucumbers that live in deep water have very elongated ambulacral legs, which they use as stilts. Other species move with the help of muscles that contract according to the type of peristalsis.

Basically, holothurians are colored black, green, sometimes with brown tones. Body length has a very wide variation, from 3 cm to 2 meters. There is also a species whose length is five meters.

Diet and lifestyle of sea cucumbers

The sea cucumber is a crawling animal that moves little. Widely distributed in any part of the ocean, at any depth. They are found in the deepest depressions, as well as on the coastline. Coral reefs are places where sea cucumbers accumulate in particularly large numbers. The dominant number of species lead a purely bottom lifestyle, however, there are also those who live in the water column or close to the surface. This lifestyle is called pelagic.

The oral end is always raised. For food, sea cucumbers consume plankton, as well as any organic remains found in the silt. They absorb them along with sand and pass them through the digestive tract, where everything is filtered. But some species perform filtration using tentacles that are covered with mucus.

During periods of severe irritation, they expel part of the intestine through the anus, as well as part of the water lungs. In this special way they protect themselves from attackers, their organs are then restored quickly. It also happens that they also throw out toxic Cuvier tubules. Holothurians often become victims of gastropods, fish, some crustaceans and starfish. An interesting fact is that fieraspheres - small fish and even crabs - can settle in their lungs.

Reproduction method and development cycle of sea cucumbers

The sexual organ of the holothurian is single, represented by the gonad, and consists of tubes collected in a bundle. The egg is most often fertilized outside the body, and development also occurs extracorporeally. Sometimes holothurians show dexterity and grab eggs with their tentacles, throwing them onto the dorsal side of the body; in exceptional cases, the egg is located inside the body.

The egg undergoes a number of changes. Metamorphoses begin with a larva capable of swimming, but the initial form, characteristic of all echinoderms, is represented by a dipleurula, which after a few days becomes an auricularia, and then a doliolaria. There are other larval forms, such as vitellaria and pentactulae, which are common to other species of holothurians. Sea cucumbers live on average 5 – 10 years.

March 24th, 2013

SEA CUCUMBERS (Holothurioidea)or sea egg pods. Sea capsules, sea cucumbers or sea cucumbers are animals whose body contracts strongly at the slightest touch, after which in many forms it becomes similar to an old capsule or cucumber. About 1,100 species of sea egg-pods are known. The name “sea cucumbers” was given to these animals by Pliny, and the description of some species belongs to Aristotle.

Holothurians are interesting due to their external features, bright colors, interesting lifestyle and some habits; in addition, they have quite a significant economic importance. Over 30 species and varieties of sea cucumbers are used by humans for food. Edible sea cucumbers, often called sea cucumbers, have long been valued as a very nutritious and medicinal dish, so fishing for these animals has been practiced since ancient times.

The main sea cucumber fisheries are concentrated mainly off the coast of Japan and China, in the waters of the Malay Archipelago, off the islands of the tropical Pacific Ocean, and near the Philippine Islands. Less significant fisheries for sea cucumbers are carried out in the Indian Ocean, in the Red Sea, off the coast of America, Africa, Australia and Italy. In the Far Eastern seas, two species of edible sea cucumbers are caught (Stichopus japonicus and Cucumaria japonica), which are used to prepare canned food and dried foods. The musculocutaneous sac of sea cucumbers, which has previously been subjected to long-term processing by boiling, drying, and in some countries, smoking, is most often consumed as food. Broths and stews are prepared from such semi-finished products. In Italy, fishermen eat fried sea cucumbers without subjecting them to complex pre-processing.

In their raw form, edible sea cucumbers are used as food in Japan, where, after removing the entrails, they are cut into slices and seasoned with soy sauce and vinegar. In addition to the skin-muscle sac, residents of Japan and the Pacific Islands use for food the intestines and gonads of edible sea cucumbers, which are more valuable. Some modern European companies produce various canned foods from sea cucumbers, which are in great demand. The world fishery for Stichopus japonicus in 1981 amounted to 8098 million tons. In addition to fishing, holothurian breeding is also practiced, in particular in our Far East. Holothurians are quite large animals, the average size of which is from 10 to 40 cm. However, among them there are also dwarf species, barely reaching a few millimeters, and real giants, whose body length with a relatively small diameter - about 5 cm - can reach 2 m, and sometimes even 5 m. In body shape, holothurians are very different from representatives of other classes of echinoderms. Most of them rather resemble large worms, but some species have an almost cylindrical or spindle-shaped, and sometimes spherical or somewhat flattened body, bearing various outgrowths on the back.

Despite this body shape, in holothurians it is almost always possible to quite clearly distinguish between the dorsal and ventral sides, although their ventral side does not morphologically correspond to that of other bilaterally symmetrical animals. They actually crawl on their sides, with their mouth end first, so the names “ventral” and “dorsal” sides are arbitrary, but quite justified. In many forms, the ventral side is more or less strongly flattened and adapted for crawling. The ventral side includes 3 radii and 2 interradii, which is why it is often called the trivium, and the dorsal side, or bivium, consists of 2 radii and 3 interradii. The location of the legs on the body of sea egg capsules further enhances the difference between the dorsal and ventral sides, since the strongly contractile legs of the trivium, concentrated on the radii or sometimes found on the interradii, are equipped with suckers and serve for the movement of the animal, while the legs of the bivium often lose motor function and are deprived suckers become thinner and already have sensitive functions. There is no separation of the head in holothurians, although in a number of forms, for example, in deep-sea representatives of the order of side-footed holothurians, one can notice some separation of the anterior end from the rest of the body, which is why it is sometimes called the head.

The mouth, devoid of any devices for grinding food and closed by the perioral sphincter, is located at the anterior end of the body or slightly shifted to the ventral side; the anus is placed at the posterior end. In relatively few forms that burrow into mud or attach to rocks, the mouth and anus move to the dorsal side, giving the animal a spherical, flask-shaped or vaulted shape. Very characteristic of all holothurians are the tentacles surrounding the mouth, which are modified ambulacral legs. The number of tentacles ranges from 8 to 30, and their structure varies among representatives of different orders. The tentacles can be tree-like branched and relatively large, covering a large area of ​​water when catching prey, or shorter, shield-shaped, resembling flowers and intended mainly for collecting nutritional material from the surface of the ground, or simple with a different number of finger-like processes, or feathery, helping with burrowing. holothurians into the ground. All of them, like the ambulacral legs, are connected to the canals of the aquifer system and are essential not only for nutrition and movement, but also for touch, and in some cases, for breathing.

Another distinctive feature of sea egg pods is that most forms have soft skin. Only a few representatives of the orders of tree-tentacled holothurians and dactylochirotids have an exoskeleton visible to the naked eye in the form of plates that fit tightly to each other and form a kind of shell. The skin skeleton of other holothurians consists of microscopic calcareous plates of a very bizarre and surprisingly beautiful shape. We can find, along with smooth plates containing a small number of holes, openwork “baskets”, “glasses”, “sticks”, “buckles”, “tennis rackets”, “turrets”, “crosses”, “wheels”, “anchors” . In addition to the skin of the body, calcareous plates can be found in the tentacles, perioral membrane, ambulacral legs, and genitals. Only a few species lack calcareous plates, but for most species they are characteristic and play an important role in identification.

The largest skeletal formation is located inside the body of the holothurian and surrounds the pharynx. The pharyngeal calcareous ring of holothurians comes in various shapes: with or without processes, solid or mosaic, etc., but, as a rule, consists of 10 pieces, 5 of which correspond to the radii of the animal, 5 to interradii. In a number of forms, the pharyngeal ring serves as the attachment point for five ribbon-like muscles (retractor muscles), which draw the anterior end of the body inward along with the tentacles. Straightening the anterior end of the body and extending the tentacles is ensured by the action of the other five ribbon-like muscles (protractor muscles) attached to the pharyngeal ring next to the retractors. The musculature of sea egg capsules is quite developed and enhances the strength of their integument; the musculocutaneous sac consists of a layer of transverse muscles and five pairs of longitudinal muscle bands located along radii.

With the help of such strong muscles, some holothurians move, burrow into the ground and strongly contract their body at the slightest irritation. The internal structure of sea egg capsules has already been considered when characterizing type A. One should, perhaps, only pay attention to a special protective device - Cuvier's organs, found in certain groups of holothurians, and to special respiratory organs - aquatic lungs. Cuvier's organs are developed in different representatives of the order of thyroid-tentacled holothurians. They are glandular tube-like formations that flow into the extension of the hind intestine - the cloaca. When an animal is irritated, they are able to be thrown out through the cloaca and stick to the irritating object. Aquatic lungs, which are absent in side-footed and legless holothurians, are also connected to the cloaca by a common duct. They are two highly branched trunks located to the left and right of the cloaca and connected to the body wall and intestinal loops by very thin muscular and connective tissue cords. Water lungs can be brightly colored orange and occupy a significant part of the animal's body cavity.

The terminal lateral branches of the pulmonary trunks form thin-walled ampulla-shaped extensions, and quite often the left aqueous lung is entangled in a network of blood vessels. The walls of the aquatic lungs are equipped with highly developed muscles, the relaxation of which leads to the expansion of the lung cavity and the drawing of sea water inward through the cloaca, and the contraction leads to the expulsion of water from the lung. Thus, thanks to the rhythmic contractions and relaxations of the cloaca and aquatic lungs, sea water fills the smallest branches of the latter, and oxygen dissolved in water penetrates through their thin walls into the fluid of the body cavity and is distributed throughout the body. Very often, substances unnecessary for the body are released through the water lungs. The thin walls of the water lungs are easily torn, and amebocytes, loaded with decay products, are expelled. Almost all holothurians are dioecious; hermaphrodites are very rare among them, and most of them are in the order of legless holothurians.

Typically, in hermaphrodites, the gonads first produce male reproductive cells - sperm, and then female reproductive cells - eggs; but there are species in which both male and female reproductive products develop simultaneously in one gonad. For example, Labidoplax buskii (from the order of legless sea cucumbers), living in the northern regions of the Atlantic Ocean, breeds off the coast of Sweden in the fall, from October to December. At this time of year, its hermaphrodite gonad contains equally mature female and male reproductive cells, but each holothurian releases eggs into the water first, and after a day or two, sperm, or vice versa. The release of reproductive products into the water can occur at intervals and in small portions. Numerous observations have shown that sea cucumbers sweep out reproductive products in the evening or at night. Apparently, darkness is a stimulus for spawning. Most often, reproduction occurs in spring or summer and is associated with temperature, but there are species in which mature reproductive products can be found throughout the year, but their maximum development, for example in Holothuria tubulosa, is observed in August or September. The timing of spawning varies not only for different species, but also for the same species if it has a large range.

Thus, the sea cucumber Cucumaria frondosa, which is very common in the Barents and Kara Seas, breeds in these seas in June - July, and off the coast of Great Britain and Norway in February - March. Typically, the reproductive products are released into the water, where the eggs are fertilized and develop. After their crushing, a free-swimming auricularium larva is formed. Many auricularia are relatively large in size - from 4 to 15 mm. In a number of sea cucumbers, the larvae, before becoming similar to the adult organism, go through one more larval barrel-shaped stage, the doliolaria, and then the last larval stage, called the pentactula. However, not all holothurians develop in this way. Nowadays, over 30 species of sea egg-pods are known that take care of their offspring and bear young. In such species, distributed mainly in cold waters, the free-swimming larval stage is lost and the eggs develop either due to a large amount of yolk or receiving nutrition directly from the mother's body. In the simplest case, eggs and young develop on the surface of the mother's body, for example, under the protection of overgrown skeletal plates, or in swollen skin folds on the back, or simply attached to the crawling sole. Further changes led to the formation of skin depressions, internal brood chambers protruding into the secondary body cavity, and in a number of branched-tentacled and legless holothurians - to the development of juveniles to late stages directly in the body cavity of the female. In all these cases, the sex of the holothurians is easily distinguishable, whereas usually this is almost impossible to do.

Giant California sea cucumber or sea cucumber Parastichopus californicus- a unique natural phenomenon. He uses the anus as a second mouth, despite the fact that he also has a real mouth.

Scientists previously knew that shallow-water marine invertebrates that live off the Pacific coast of North America use the anus for breathing. Since they do not have lungs, they use the water vascular system for breathing. ambulacral system, which consists of many channels running throughout the body. The branched sacs with which sea cucumbers breathe receive oxygen when water is pumped into the anus using the rectal muscles.

Giant sea cucumber

Half-meter-long sea cucumbers, which lead a predominantly sedentary lifestyle and are even permanent homes for some small inhabitants of the seabed, can pump up to 800 milliliters of water every hour. The body of these animals sifts out oxygen from the remaining components of sea water and saturates its cells with it.

Dr. William Jaeckle from Illinois Wesleyan University and Richard Strathmann from the University of Washington decided to study these amazing creatures in more detail.

They found that the system of blood vessels connecting the respiratory branched sacs with the intestines (the so-called rete mirabile), is not intended to transport oxygen to the intestines. From a scientific point of view, it would be more logical to assume that this structure is needed to transfer food from the anus to the intestines, and not vice versa, as is usually the case in animals. Zoologists decided to test their hypothesis.

To confirm their hypothesis, the researchers fed several giant sea cucumbers radioactive algae that contained iron particles. Using this trick, the team was able to trace the entire path that food takes through the echinoderm's body. In addition, radioactive particles accumulate in the part of the body where the opening through which the creatures consume food is located.

The results of the study demonstrated that sea cucumbers feed primarily through the mouth. But high concentrations of radioactive particles and iron were also observed in the structure of the rete mirabile, which proves that sea cucumbers use the anus as a second mouth. It turns out that the anus of these creatures performs three vital functions: respiratory, nutritional and excretory.

Scientists say that studying just one species of sea cucumber does not mean that only they use a bipolar method of feeding. Later, zoologists intend to study other species of echinoderms.

The study was published in the March issue of the journal Invertebrate Biology.

Among the numerous species of sea cucumbers, the most valuable for fishing are sea cucumber and cucumber. Sea cucumber and cucumber are similar in body structure and the chemical composition of the meat. Trepang contains biologically valuable substances (stimulants), for which in Eastern countries it is called the sea root of life (ginseng) and is widely recommended for those suffering from loss of physical strength and increased fatigue. Eating sea cucumber helps strengthen the nervous system. Sea cucumber fishing is carried out in spring and autumn only in the Far East. The caught sea cucumbers are cut up at the fishing site - the abdomen is cut and the entrails are removed. Cleaned sea cucumbers are washed and boiled for 2-3 hours until the meat becomes soft, after which it is used for preparing culinary dishes.

Skoblyanka with sea cucumber in tomato sauce.
Cut the boiled sea cucumbers into small pieces and fry in oil along with onion, flour and tomato paste. Mix everything, put it in a saucepan, add a little water and boil for 10-15 minutes over low heat.
400 g sea cucumbers, 3/4 cup oil, 3 onions, 4-5 tablespoons of tomato paste, 2 tbsp. spoons of flour, 4 tbsp. spoons of water, salt to taste.

Sea cucumbers fried with onions.
Chop the sea cucumbers and onions and fry them separately, then mix, add spices and serve hot. Sprinkle green onions on top.
400 g sea cucumbers, 2 heads of onions, 1/2 cup vegetable oil, 1 teaspoon allspice, 100 g green onions, salt to taste.

Stewed sea cucumbers.
Melt the butter in a frying pan and add the boiled sea cucumbers cut into pieces and simmer for 3 minutes. Add milk, salt, pepper and bring almost to a boil. Serve, garnished with red pepper.
250 g sea cucumbers, 4 tbsp. spoons of margarine or vegetable oil, 1 tbsp. a spoonful of milk, black pepper, red pepper, salt to taste.

Sea cucumbers with vegetables.
Cut the boiled sea cucumbers into pieces and fry. Chop fresh cabbage, chop vegetables (potatoes, carrots, zucchini, tomatoes) and mix with sea cucumbers, put in a saucepan and simmer over low heat until the vegetables are ready.
300 g sea cucumber, 1/4 fork fresh white cabbage, 3-4 pcs. potatoes, 1-2 carrots, 1-2 zucchini, 1 glass of oil, 2-3 tomatoes or 2 tbsp. spoons of tomato paste, pepper, sugar, salt to taste.

Trepangs stewed with chicken.
Place the boiled sea cucumbers in a bowl with boiled or fried chicken, season with the prepared sauce and simmer over low heat until cooked.
200-300 g sea cucumbers, 1/2 chicken. For the sauce: 1-2 tbsp. spoons of tomato puree, 1 tbsp. spoon of 3% vinegar, 2 tbsp. spoons of wine (port or Madeira), 2-3 tbsp. spoons of butter, 1/2 cup of meat broth.

Trepangs with horseradish.
Boiled sea cucumbers are cut into slices. Dilute the vinegar with water, add grated horseradish, salt, sugar and bring to a boil. Then pour in boiled, chopped slices of sea cucumber. The dish is served cold.
Boiled sea cucumbers 70, table vinegar 40, grated horseradish 10, sugar 2, salt

Clean the sea cucumber and pour boiling water over it. After about 1 minute, drain the water and cut the sea cucumber into pieces.
Sauce: soy sauce 2 tbsp, garlic 3 cloves (squeeze), mayonnaise 1 tbsp. Mix all. Delicious.

Salad with sea cucumber.
Boiled sea cucumbers are cut into small pieces, boiled potatoes are cut into cubes, green peas, chopped eggs are added, lemon juice and salt are added. All products are mixed, then seasoned with mayonnaise and decorated with green salad and egg.
Boiled sea cucumber 80, potatoes 80, egg 0.5 pcs., green peas 40, mayonnaise sauce 40, lemon juice, salt.

Holothurians, or sea capsules, or sea cucumbers (lat. Holothuroidea) - this is the name of animals whose body contracts strongly at the slightest touch, after which in many forms it becomes similar to an old capsule or cucumber. About 1,100 species of sea egg-pods are known. The name “sea cucumbers” was given to these animals by Pliny, and the description of some species belongs to Aristotle.

Holothurians are interesting due to their external features, bright colors, interesting lifestyle and some habits; in addition, they have quite a significant economic importance. Over 30 species and varieties of sea cucumbers are used by humans for food. Edible sea cucumbers, often called sea cucumbers, have long been valued as a very nutritious and medicinal dish, so fishing for these animals has been practiced since ancient times.

The main sea cucumber fisheries are concentrated mainly off the coast of Japan and China, in the waters of the Malay Archipelago, off the islands of the tropical Pacific Ocean, and near the Philippine Islands. Less significant fisheries for sea cucumbers are carried out in the Indian Ocean, in the Red Sea, off the coast of America, Africa, Australia and Italy. In the Far Eastern seas, two species of edible sea cucumbers are caught (Stichopus japonicus and Cucumaria japonica), which are used to prepare canned food and dried foods. The musculocutaneous sac of sea cucumbers, which has previously been subjected to long-term processing by boiling, drying, and in some countries, smoking, is most often consumed as food. Broths and stews are prepared from such semi-finished products. In Italy, fishermen eat fried sea cucumbers without subjecting them to complex pre-processing.

In their raw form, edible sea cucumbers are used as food in Japan, where, after removing the entrails, they are cut into slices and seasoned with soy sauce and vinegar. In addition to the skin-muscle sac, residents of Japan and the Pacific Islands use for food the intestines and gonads of edible sea cucumbers, which are more valuable. Some modern European companies produce various canned foods from sea cucumbers, which are in great demand. The world fishery for Stichopus japonicus in 1981 amounted to 8098 million tons. In addition to fishing, holothurian breeding is also practiced, in particular in our Far East.

Holothurians are quite large animals, the average size of which is from 10 to 40 cm. However, among them there are also dwarf species, barely reaching a few millimeters, and real giants, whose body length with a relatively small diameter - about 5 cm - can reach 2 m, and sometimes even 5 m. In body shape, holothurians are very different from representatives of other classes of echinoderms. Most of them rather resemble large worms, but some species have an almost cylindrical or spindle-shaped, and sometimes spherical or somewhat flattened body, bearing various outgrowths on the back.

Despite this body shape, in holothurians it is almost always possible to quite clearly distinguish between the dorsal and ventral sides, although their ventral side does not morphologically correspond to that of other bilaterally symmetrical animals. They actually crawl on their sides, with their mouth end first, so the names “ventral” and “dorsal” sides are arbitrary, but quite justified. In many forms, the ventral side is more or less strongly flattened and adapted for crawling. The ventral side includes 3 radii and 2 interradii, which is why it is often called the trivium, and the dorsal side, or bivium, consists of 2 radii and 3 interradii. The location of the legs on the body of sea egg capsules further enhances the difference between the dorsal and ventral sides, since the strongly contractile legs of the trivium, concentrated on the radii or sometimes found on the interradii, are equipped with suckers and serve for the movement of the animal, while the legs of the bivium often lose motor function and are deprived suckers become thinner and already have sensitive functions. There is no separation of the head in holothurians, although in a number of forms, for example, in deep-sea representatives of the order of side-footed holothurians, one can notice some separation of the anterior end from the rest of the body, which is why it is sometimes called the head.

The mouth, devoid of any devices for grinding food and closed by the perioral sphincter, is located at the anterior end of the body or slightly shifted to the ventral side; the anus is placed at the posterior end. In relatively few forms that burrow into mud or attach to rocks, the mouth and anus move to the dorsal side, giving the animal a spherical, flask-shaped or vaulted shape. Very characteristic of all holothurians are the tentacles surrounding the mouth, which are modified ambulacral legs. The number of tentacles ranges from 8 to 30, and their structure varies among representatives of different orders. The tentacles can be tree-like branched and relatively large, covering a large area of ​​water when catching prey, or shorter, shield-shaped, resembling flowers and intended mainly for collecting nutritional material from the surface of the ground, or simple with a different number of finger-like processes, or feathery, helping with burrowing. holothurians into the ground. All of them, like the ambulacral legs, are connected to the canals of the aquifer system and are essential not only for nutrition and movement, but also for touch, and in some cases, for breathing.

Another distinctive feature of sea egg pods is that most forms have soft skin. Only a few representatives of the orders of tree-tentacled holothurians and dactylochirotids have an exoskeleton visible to the naked eye in the form of plates that fit tightly to each other and form a kind of shell. The skin skeleton of other holothurians consists of microscopic calcareous plates of a very bizarre and surprisingly beautiful shape.

We can find, along with smooth plates containing a small number of holes, openwork “baskets”, “glasses”, “sticks”, “buckles”, “tennis rackets”, “turrets”, “crosses”, “wheels”, “anchors” . In addition to the skin of the body, calcareous plates can be found in the tentacles, perioral membrane, ambulacral legs, and genitals. Only a few species lack calcareous plates, but for most species they are characteristic and play an important role in identification.

The largest skeletal formation is located inside the body of the holothurian and surrounds the pharynx. The pharyngeal calcareous ring of holothurians comes in various shapes: with or without processes, solid or mosaic, etc., but, as a rule, consists of 10 pieces, 5 of which correspond to the radii of the animal, 5 to interradii. In a number of forms, the pharyngeal ring serves as the attachment point for five ribbon-like muscles (retractor muscles), which draw the anterior end of the body inward along with the tentacles.

Straightening the anterior end of the body and extending the tentacles is ensured by the action of the other five ribbon-like muscles (protractor muscles) attached to the pharyngeal ring next to the retractors. The musculature of sea egg capsules is quite developed and enhances the strength of their integument; the musculocutaneous sac consists of a layer of transverse muscles and five pairs of longitudinal muscle bands located along radii.

With the help of such strong muscles, some holothurians move, burrow into the ground and strongly contract their body at the slightest irritation. The internal structure of sea egg capsules has already been considered when characterizing type A. One should, perhaps, only pay attention to a special protective device - Cuvier's organs, found in certain groups of holothurians, and to special respiratory organs - aquatic lungs. Cuvier's organs are developed in different representatives of the order of thyroid-tentacled holothurians. They are glandular tube-like formations that flow into the extension of the hind intestine - the cloaca.

When an animal is irritated, they are able to be thrown out through the cloaca and stick to the irritating object. Aquatic lungs, which are absent in side-footed and legless holothurians, are also connected to the cloaca by a common duct. They are two highly branched trunks located to the left and right of the cloaca and connected to the body wall and intestinal loops by very thin muscular and connective tissue cords. Water lungs can be brightly colored orange and occupy a significant part of the animal's body cavity.

The terminal lateral branches of the pulmonary trunks form thin-walled ampulla-shaped extensions, and quite often the left aqueous lung is entangled in a network of blood vessels. The walls of the aquatic lungs are equipped with highly developed muscles, the relaxation of which leads to the expansion of the lung cavity and the drawing of sea water inward through the cloaca, and the contraction leads to the expulsion of water from the lung. Thus, thanks to the rhythmic contractions and relaxations of the cloaca and aquatic lungs, sea water fills the smallest branches of the latter, and oxygen dissolved in water penetrates through their thin walls into the fluid of the body cavity and is distributed throughout the body. Very often, substances unnecessary for the body are released through the water lungs. The thin walls of the water lungs are easily torn, and amebocytes, loaded with decay products, are expelled. Almost all holothurians are dioecious; hermaphrodites are very rare among them, and most of them are in the order of legless holothurians.

Typically, in hermaphrodites, the gonads first produce male reproductive cells - sperm, and then female reproductive cells - eggs; but there are species in which both male and female reproductive products develop simultaneously in one gonad. For example, Labidoplax buskii (from the order of legless sea cucumbers), living in the northern regions of the Atlantic Ocean, breeds off the coast of Sweden in the fall, from October to December. At this time of year, its hermaphrodite gonad contains equally mature female and male reproductive cells, but each holothurian releases eggs into the water first, and after a day or two, sperm, or vice versa.

The release of reproductive products into the water can occur at intervals and in small portions. Numerous observations have shown that sea cucumbers sweep out reproductive products in the evening or at night. Apparently, darkness is a stimulus for spawning. Most often, reproduction occurs in spring or summer and is associated with temperature, but there are species in which mature reproductive products can be found throughout the year, but their maximum development, for example in Holothuria tubulosa, is observed in August or September. The timing of spawning varies not only for different species, but also for the same species if it has a large range.

Thus, the sea cucumber Cucumaria frondosa, which is very common in the Barents and Kara Seas, breeds in these seas in June - July, and off the coast of Great Britain and Norway in February - March. Typically, the reproductive products are released into the water, where the eggs are fertilized and develop. After their crushing, a free-swimming auricularium larva is formed. Many auricularia are relatively large in size - from 4 to 15 mm. In a number of sea cucumbers, the larvae, before becoming similar to the adult organism, go through one more larval barrel-shaped stage, the doliolaria, and then the last larval stage, called the pentactula.

However, not all holothurians develop in this way. Nowadays, over 30 species of sea egg-pods are known that take care of their offspring and bear young. In such species, distributed mainly in cold waters, the free-swimming larval stage is lost and the eggs develop either due to a large amount of yolk or receiving nutrition directly from the mother's body. In the simplest case, eggs and young develop on the surface of the mother's body, for example, under the protection of overgrown skeletal plates, or in swollen skin folds on the back, or simply attached to the crawling sole. Further changes led to the formation of skin depressions, internal brood chambers protruding into the secondary body cavity, and in a number of branched-tentacled and legless holothurians - to the development of juveniles to late stages directly in the body cavity of the female. In all these cases, the sex of the holothurians is easily distinguishable, whereas usually this is almost impossible to do.

Half-meter-long sea cucumbers, which lead a predominantly sedentary lifestyle and are even permanent homes for some small inhabitants of the seabed, can pump up to 800 milliliters of water every hour. The body of these animals sifts out oxygen from the remaining components of sea water and saturates its cells with it.

Dr. William Jaeckle from Illinois Wesleyan University and Richard Strathmann from the University of Washington decided to study these amazing creatures in more detail.

They found that the system of blood vessels connecting the respiratory branched sacs with the intestines (the so-called rete mirabile) is not intended to transport oxygen to the intestines. From a scientific point of view, it would be more logical to assume that this structure is needed to transfer food from the anus to the intestines, and not vice versa, as is usually the case in animals. Zoologists decided to test their hypothesis.

To confirm their hypothesis, the researchers fed several giant sea cucumbers radioactive algae that contained iron particles. Using this trick, the team was able to trace the entire path that food takes through the echinoderm's body. In addition, radioactive particles accumulate in the part of the body where the opening through which the creatures consume food is located.

The results of the study demonstrated that sea cucumbers feed primarily through the mouth. But high concentrations of radioactive particles and iron were also observed in the structure of the rete mirabile, which proves that sea cucumbers use the anus as a second mouth. It turns out that the anus of these creatures performs three vital functions: respiratory, nutritional and excretory.

Scientists say that studying just one species of sea cucumber does not mean that only they use a bipolar method of feeding. Later, zoologists intend to study other species of echinoderms.

Among the numerous species of sea cucumbers, the most valuable for fishing are sea cucumber and cucumber. Sea cucumber and cucumber are similar in body structure and the chemical composition of the meat. Trepang contains biologically valuable substances (stimulants), for which in Eastern countries it is called the sea root of life (ginseng) and is widely recommended for those suffering from loss of physical strength and increased fatigue. Eating sea cucumber helps strengthen the nervous system. Sea cucumber fishing is carried out in spring and autumn only in the Far East. The caught sea cucumbers are cut up at the fishing site - the abdomen is cut and the entrails are removed. Cleaned sea cucumbers are washed and boiled for 2-3 hours until the meat becomes soft, after which it is used for preparing culinary dishes.

Scientific classification:
Domain: Eukaryotes
Kingdom: Animals
Type: Echinoderms
Class: Holothurians (lat. Holothuroidea (Blainville, 1834))

Sea cucumbers: appearance

Representatives of the class of holothurians have an elongated, worm-shaped body, similar to a thick caterpillar. They can reach quite large sizes. The largest of them are up to 5 m long.

At one end of the animal’s body there is a mouth opening, at the other there is a powder. The front side of its body is called the oral pole, and the back side is called the aboral pole.

The holothurian's mouth is surrounded by many tentacles that help catch and absorb food. Their length is different. They can be small in size, but in some species they grow very long and branched, forming a whole bush around the mouth.

Leopard sea cucumber

Sea cucumbers move in the same way as most echinoderms, using ambulacral legs that are located on the underside of their body. Swimming species do not have such legs, but move by bending the body.

Usually the color of these sea inhabitants is not too bright; brown, off-white and grayish colors predominate. But sometimes there are also very beautifully colored species.

Holothurians: way of life

Most representatives of the class of holothurians are bottom dwellers. They crawl along the bottom and even burrow into the ground, looking for food: organic remains and small planktonic organisms. These animals move slowly.

Some species lead an almost immobile lifestyle. They are called tree-tentacled ( Dendrochirota), as they catch food using their highly branched tentacles.

Planktonic species swim in the water column. They do not have legs for movement, but are shaped like a disk with several outgrowths along the edges. They live up to 10 years.

Holothurian class: internal structure

The skeleton of these animals consists of individual small calcareous inclusions of various shapes. A calcareous ring is formed around the pharynx, which serves as a site for muscle attachment. Their muscles are very strong, which compensates for their underdeveloped skeleton.

In the body, under the outer covering there is a continuous layer of so-called circular muscles, and then 5 longitudinal muscle bands. Under the muscles there is a body cavity - the whole, where the internal organs are located.

The alimentary canal is a long cylindrical tube of considerable length. It expands near the posterior pole, forming a cloaca.

Special Cuvier organs are located here, which look like long sticky threads and are used to scare away enemies. At the moment of danger, they are thrown out, entwining a foreign object.

Animals that make up the class Holothuria breathe with the help of two water lungs. These voluminous branched organs have an opening directly connected to the cloaca, through which water enters and then pours out.

Sea cucumbers have a highly branched circulatory system. It is distinguished by a large number of blood vessels in the intestinal area. A network of vessels densely entwines the tissues of the left lung, so oxygen from it enters the blood, in contrast to the right, which supplies oxygen to the cavity fluid.

The basis of the nervous system is the peripharyngeal nerve ring, from which 5 radial nerves extend in different directions. They are located in special epineural canals. Holothurians have tentacles as their sensory organs. They do not have light-sensitive eyes. And some species have statocysts - organs of balance.

The excretory system of these animals is diffuse. The end products of sea cucumbers accumulate in amoebocytes, which then exit the body through the outer integument.

Reproduction and development

Representatives of the class of holothurians are both hermaphrodites and dioecious. They have one gonad, which looks like branched tubes. This is where eggs and sperm mature. Reproductive products are released into the surrounding water through a special genital duct.

The development of the larva takes place in three stages: dipleurula, auricularia and vdoliolaria. Holothurian larvae are swimming organisms. In the process of growth and development, they settle to the bottom and turn into adult animals. At the same time, their structure changes radically.

The class of holothurians unites marine animals that are not only very interesting, but also of significant economic importance for people. About 40 of their species are used as food. Fishing for edible sea cucumbers or sea cucumbers is carried out in the waters of Indonesia, the Philippines, and off the coast of Japan and China. In the Pacific Ocean they are mined at a rate of over 10 thousand centners per year.

And this video will introduce you in more detail to these interesting multicellular animals, which have the interesting name “sea cucumbers”:

“Sea cucumber” is an unusual inhabitant of the underwater world. It somewhat resembles a worm, or more precisely, a large, thick caterpillar. This “vegetable” has a very specific way of protecting itself from enemies - it sprays its internal organs onto them.

These invertebrates can be found in almost all seas except the Caspian and Baltic. They live both in coastal areas and in deep-sea depressions. Coral reefs serve as their main home.

Holothurians, depending on the species, have different sizes, ranging from 0.5 centimeters to 5 meters (for example, spotted synapta). In addition to being the longest among the other species, it is also the fastest.

The length of most sea cucumbers varies from 3 centimeters to 1-2 meters. They come in incredible colors, ranging from speckled brown to bright yellow with orange and blue stripes.

Externally, “sea cucumbers” look more like large and clumsy caterpillars. Their soft body can be smooth, rough, or covered with various outgrowths.

On one side of the body, they have a mouth, and on the other, an anus, which also serves as a “sea cucumber” for ...... breathing! This was the first time I heard that this was even possible. With its help, sea cucumbers draw in water saturated with oxygen. From there, the water enters the water lungs, which are located next to the anus.

Her mouth is surrounded by tentacles, with which she puts food into her mouth. During its leisurely movement, the holothurian touches the sand, silt or corals with its tentacles and captures from them the smallest particles of organic matter and grains of sand with bacteria. Because of this “sandy diet,” the sea cucumber constantly emptys its intestines. In addition to organic matter and bacteria, it feeds on plankton.

These invertebrates move slowly, contracting and stretching their bodies. Some species are able to swim using worm-like movements.

Holothuria almost always lies on one side of the body – the trivium. If you turn it over, it will definitely return to its original position.

Reproduction in sea cucumbers occurs sexually. Females lay eggs directly in the water, and the male fertilizes them. Some species are caring parents. For example, the red holothurian, which lives off the coast of California, carries eggs on its back under calcareous plates. When ripe, the larvae break through the mother's skin and begin to swim freely.

The larvae go through 3 stages of development: 1 - dipleurula, 2 - auricularia and the final stage - doliolaria. During the first month of their life, they feed on single-celled algae.

Holothuria is a unique animal. She can easily say goodbye to part of her body. When strongly irritated or touched, she throws out her insides through the anus: the back of the intestine, the water lungs and the Cuvier's bundles - organs containing toxins. Scientifically, this phenomenon is called evisceration.

Regeneration of lost organs occurs quite quickly and is completely completed in 6-8 weeks. In addition, these animals can reproduce their body from half or even one quarter of what remains of it. True, they no longer grow to their original size.

And finally. Holothuria is a walking home for the tiny “pearl” fish Carapus affinis, which lives in its anus. Here the fish are always protected and supplied with a supply of fresh water. It must be funny to watch the fish stick its head out of this hole.