Which are called "ship worms". No, we were not mistaken - such animals really exist.
Shipworm: animal class and type
The thing is that the shipworm, which is also called teredo, or woodworm, has undergone significant changes in the course of evolution. They especially concern external structure animal. Therefore, at first glance, it is quite difficult to figure out which class the shipworm belongs to. This is actually a representative and the Class that the shipworm represents is called "Bivalves".
External structure
Teredo has a cylindrical body that reaches a length of about a meter. Since the shipworm belongs to the class of bivalve mollusks, it has structural features inherent to them. Where is his shell? It is located at the anterior end of the body and consists of two small valves about 1 cm in size. With their help, the mollusk drills into wood. Each valve is formed by three parts with jagged edges.
Otherwise, the shipworm mollusk has structural features typical of this systematic unit. Its body is flattened laterally and consists of two sections: the torso and legs. Since they do not have a head, they also lack organs located on it. pharynx, tongue with a grater, jaws and salivary glands. The mantle covers the back of their body. There are also glands that secrete calcareous substances.
Almost the entire body of a shipworm is located in wood. On the surface it leaves only the rear end with a pair of siphons. Through them the relationship between the animal and environment. The teredo protection mechanism is also interesting. Along with the siphons, at the posterior end of the body there is a plate made of the solid carbohydrate chitin. In case of danger, the animal pulls the siphons into the tree passage. And the hole is closed with a chitinous plate.
Habitat
All bivalves live in water. They can be found in all seas, excluding only the coldest ones. This is due to the fact that they feed by filtration. The shipworm passes through siphons water with organic residues that are in it. Another teredo is wood. Using a reduced shell, they make passages in it. Therefore, teredos live in the wood of piers and ships, driftwood that has fallen to the bottom, and rhizomes marine plants.
Internal structure
Like all mollusks, shipworms have a secondary body cavity. However, the spaces between the organs are filled with loose connective tissue. Circulatory system these animals are not closed. It consists of the heart and blood vessels. Blood from the arteries enters the body cavity. Here it mixes with liquid and washes all organs. At this stage, gas exchange occurs. Blood enters the heart through the veins. The shipworm is a cold-blooded animal. Therefore, living in a very cold water he can not.
The woodworm's respiratory organs are gills, with the help of which it absorbs oxygen from the water. Excretory system represented by the kidneys. They secrete metabolic products into the perimantle cavity. The shipworm has nervous system scattered-nodular type.
Features of life
Shipworms are in constant action. They make about ten drilling movements per minute. At the same time, they push the doors apart, which destroy the wood with their jagged edges. The size of the shipworm's passages increases as the animal itself grows. They can reach 2 meters in length with a diameter of 5 cm. Another name for them is associated with this way of life - wood borers. The surprising fact is that the passages of these mollusks never intersect. Scientists suggest that they hear the approaching sounds of their “neighbor” drilling and change their direction. This is the kind of respect animals show to each other!
Certain enzymes are required to digest the complex carbohydrate cellulose, which makes up wood. Teredo are not able to produce them on their own. The peculiarity of their structure digestive system is the presence of a long blind outgrowth of the stomach, in which sawdust constantly accumulates. Symbiotic bacteria live here. They break down cellulose into the monosaccharide glucose. Another function of symbionts is the fixation of nitrogen in the water.
Reproduction and development
Shipworms are hermaphrodites. This means that one individual produces both male and female reproductive cells. Fertilized eggs are first found in the gill cavity, where they develop for up to 3 weeks. From them the larvae develop. They go out into the water and swim here for another 2 weeks. The leg of the mollusk begins to secrete a special protein substance in the form of a thread - bysus. With its help, the larva attaches to the wood. During this period Teredo has a typical appearance bivalve mollusk. Most of its body is hidden by shells, from which a leg protrudes noticeably. As the animal develops, it becomes worm-like.
Meaning in nature and human life
Shipworms have rightfully earned a bad reputation. They really do a lot of damage, destroying wood with their moves. These animals were especially dangerous in ancient times, when people did not yet know about methods of dealing with them. Shipworms can completely destroy the bottom or sides of a ship, turn the supports of bridges and piers into dust, and cause the death of marine plants. Nowadays, wood that can become a “victim” of shipworms is covered with special toxic substances, which make it “inedible” for these mollusks.
So, shipworms, despite their name, are representatives of the class “Bivalves”. They live in almost all seas, settling on woody objects. These animals have an elongated soft body and two reduced shell valves. With their help, they make moves in the wood, thereby destroying it and causing great harm.
The changes in the structure of the body and shell that the troupe of mollusks called shipworms, or woodworms, have undergone are so profound that many of them have lost their original appearance bivalves.
Such is the shipworm (Teredo), which in fact, of course, is not a worm, but a mollusk. It got its name as a worm because of its long, naked body. A small shell of a peculiar structure plays the role of a drill and is located at the anterior end of the body.
Structure of a shipworm
The structure of a shipworm is a shining example adaptation to changed living conditions. Common habitats for teredos include pieces of wood, pier piles, wooden ships, rhizomes of marine plants, and even sunken coconuts in the sea. Shipworms have the most advanced adaptations for boring holes in wood. The mollusk covers the hole drilled in the tree with calcareous secretions of the mantle, resulting in the formation of a protective tube. At the posterior end of the body of the teredo there are two long thin siphons - inspiratory and expiratory. They can be strongly extended from the passage and serve to connect the mollusk with external environment: Primarily for breathing and nutrition.
By counting the number of pairs of siphons protruding from small holes in the wood, it is possible to determine how many teredo individuals lead to this place destructive work. In addition to siphons, at the posterior end of the body there are peculiar chitinous plates. When the siphons are moved outward from the passage hole, the plates are pulled inward. At the slightest danger, the mollusk retracts the siphons and plugs the opening of the passage with chitinous plates. The passage gradually expands inward from the inlet hole, and the hole itself is so small that the plates easily close it.
A small, strong shell covers only the very front end of the mollusk’s body. In an adult woodworm, the shell occupies only 1/30-1/40 of the body length. Between the widely spread shell valves, a small rounded leg emerges in front, and an elongated soft body emerges from behind.
Sink flaps serve as excellent tools for drilling into wood. The front part of the shell projects forward in the form of an ear with horizontal, finely serrated ridges. The middle part is covered with powerful ridges with coarser teeth. These ridges are located at right angles to the front ridges. Rear end shells are smooth. Moving and spreading the valves, the mollusk rubs its combs along the wood and grinds its way like a drill. The teredo produces drilling movements rhythmically 8-12 times per minute. It is interesting that neighboring passages of woodworms never intersect, no matter how densely they pass through the wood infected by them. Apparently, the worms somehow perceive the drilling sounds coming from the neighboring passage, and make turns in their passage so as not to collide with their neighbor. Such bending of the passages leads to even greater riddling of the wood.
How do shipworms feed?
As befits bivalves, shipworms filter feed on sea plankton, sucking water through the inlet siphon, as well as sawdust, which is scraped off when drilling.
Due to feeding on wood, which is very difficult to digest, the stomach of the Teredo has a large blind sac-like outgrowth, always filled with sawdust. Pieces of wood scraped off by the shell are swallowed through the mouth and enter the stomach. There they are absorbed by amebocytes and digested intracellularly. The shipworm belongs to an exceptionally small group of animals that have an enzyme that breaks down cellulose, turning it into glucose. As you remember, some ciliates and flagellates have such enzymes.
Reproduction of shipworms
Shipworms are bisexual organisms, but each individual, when it begins to reproduce, first produces sperm and then eggs. This alternation excludes self-fertilization. Sometimes eggs can develop without fertilization, parthenogenetically. Fertilized eggs first develop inside the gill cavity of an adult mollusk: after 20-30 hours, a trochophore larva is formed, and after another 36-48 hours, a veliger larva is formed. Only after 2-3 weeks the veliger comes out into the water, where it floats freely with the help of a sail for 2-2.5 weeks. Veliger has exactly the same appearance as all other mollusks. Having found a piece of wood, it settles, attaching itself with the help of a byssus. At this moment, the shipworm still looks like an ordinary bivalve mollusk: its shell is normally developed and covers the entire body, protruding forward long leg, and short siphons stick out slightly from the shell at the back. The leg is capable of secreting a byssus, with the help of which the veliger is attached to the tree. Further development turns the teredo into a “worm”, unlike an ordinary mollusk.
Measures to combat shipworms
Shipworms are dangerous pests of wooden piles, piers, and underwater parts of wooden ships. In past centuries, when all ships were built of wood, shipworms were terrible enemies of the fleet, completely wearing out the bottoms and sides of ships. Marine wood borers are very widespread and are found in almost all seas of both hemispheres, being absent only in cold Arctic waters. Teredo navalis (up to 25 centimeters long) is found in the Black and Baltic Seas; Nototeredo norvegica (up to 50 centimeters long) and the even larger T. megotara live in the Barents Sea. Several species of small shipworms also live in the Far Eastern seas.
Measures to combat ship woodworms are very diverse, but mainly come down to covering underwater wooden structures with varnishes, paints, and impregnating the wood with substances toxic to mollusks - creosote, coal varnish, carbolic acid.
Few modern sailors know that just over a century ago, one of the main threats to shipping was not violent storms, treacherous shoals and reefs, or ferocious pirates, but a peculiar sea creature, known as the shipworm or blackbird (according to explanatory dictionary Russian language by V. Dahl, “to play tricks” means to tinker or fuss)...
This animal could destroy a completely new ship in just two or three months, turning its wooden bottom literally into a sieve. But it was not only the fleet that suffered from the shipworm. Any tree immersed in water quickly became unusable. But until the beginning of the 20th century most Marine structures such as jetties, embankments and piers were made of wood. In 1731-1732 a ship worm, having suddenly multiplied in unprecedented numbers off the coast of Holland, rendered it unusable wooden piles dams, due to which two provinces of this country were under the threat of flooding.
It was then that the Dutch scientist Gottfried Zell, who began studying the shipworm at the request of coastal residents, was the first to find out that in fact this sea creature was not a worm at all, but a bivalve mollusk, the shell of which had changed and turned into a device for drilling wood. Today, about 70 species of marine wood-boring mollusks are known, which are widespread in tropical and temperate regions of the World Ocean with water salinity above 10%, including in the Black, Azov and Far Eastern seas. The natural settlements of these animals are associated with mangroves and woody debris carried into the sea by rivers. But as soon as a person began to master marine environment, wood-boring mollusks began to settle in the underwater parts of wooden ships and various hydraulic structures, boring passages into them and thus destroying them.
Shipworms have adapted to a very peculiar way of life. Adults of these mollusks live in passages that they bore into wood using their modified shells. They have a worm-shaped cylindrical body up to 0.5-1.5 m long (hence the name shipworm), at the rear end of which there are two thin long siphons with a pair of calcareous plates at the base. The latter serve to protect the body of the mollusk and close the small entrance hole when the animal drills into wood. At the front end there is a relatively small (up to 1 cm), but very strong bivalve shell with serrations, which is an excellent tool for drilling wood. During this process, the mollusk attaches to the wall of the passage with the help of its legs, opens the valves slightly and makes rhythmic movements with them (from 8 to 12 times per minute), during which they, like a rasp, tear off a layer of wood. The walls of the passage are lined from the inside by the mollusk with a thin layer of calcareous deposits. It is interesting to note that, no matter how densely shipworms populate the wood, their passages never intersect, so a heavily affected piece of wood in cross section resembles a honeycomb. Since shipworms enter wood in the larval stage, their entry holes are microscopic in size and hardly noticeable. Therefore, it often turns out that the wood is completely riddled, although at first glance it looks completely unharmed. The course of the shipworm increases as it grows and can reach 2 m in length and 5 cm in diameter.
These mollusks feed on organic debris and small plankton, which are filtered from the water sucked through siphons, as well as by processing sawdust formed during drilling. Shipworms are hermaphrodites (i.e., periodically functioning as males or females) and are very fertile. Three to four times a year they produce from 1 to 5 million eggs, which develop in the gill chamber of the animal that gave birth to them for about two weeks. The larvae emerging from the eggs leave the mother’s body and initially live in the water column. After one to three weeks, they find something wooden immersed in water and attach themselves to it with byssal threads. Immediately, after quickly transforming into a tiny and seemingly ordinary bivalve mollusk, young individuals of shipworms begin to scrape the wood with the sharp edges of the shell. Having scraped up a small pile of sawdust, they cover themselves with it like a hut. Young mollusks protected in this way change their appearance beyond recognition in a few days - their body narrows and takes on a worm-like shape, like that of their parents. After this, they penetrate the tree and begin the life of a shipworm. The young grow quickly and within three months become capable of producing offspring.
Since shipworms have caused enormous damage to shipping and various hydraulic structures, people were constantly looking for effective means fight them. In addition to covering the bottoms with special poisonous paints, long years Regular entry of wooden ships into rivers was widely practiced (draining for a month had a good effect), especially during the period of breeding of shipworms and the settling of their larvae, which are very sensitive to desalination. In the end, although this made the ships more expensive and heavier, shipowners began to sheathe their bottoms with lead and copper sheets, because no tree could withstand the drilling force of the shipworm valves. But all this was of little use until toxic chemical impregnations for wood were invented (primarily creosote), then they completely switched to steel shipbuilding.
Although shipworms usually avoid coastal waters with low salinity, since the beginning of the 1990s, hornet began to actively spread along the Danish and German coasts Baltic Sea. IN last years there was a threat of its penetration into the Swedish coast. Scientists believe that the expansion of the geographical range of this shipworm is due to climate change, that is, rising water temperatures help the mollusk adapt to conditions of lower salinity. In connection with its appearance in the Baltic Sea, there is a great threat to the remains of wooden ships that sank here centuries ago, because until now they remained undestroyed only because the hornet never lived in these waters. In the neighboring North Sea and Atlantic, where it is found in abundance, this shipworm has caused significant damage to many wooden shipwrecks of archaeological value. Despite all this, we should not forget that carpenter mollusks play important role processors of any wood that ends up at sea.
The products of their vital activity and they themselves become food objects for various marine organisms. Some types of shipworms in countries South-East Asia They are specially bred to be used as food, because they are the same molluscs as oysters and mussels.
Shipworms or woodworms, belonging to the family of mollusks, have undergone such changes in the process of evolution that they have completely lost their external resemblance to bivalve mollusks.
The Teredo shipworm is not actually a worm, it is a mollusk. The mollusk began to be called a worm due to its long body.
A small shell is located at the anterior end of the body and functions as a drill.
Structure of a shipworm
Due to changing living conditions, the structure of the shipworm has also changed. The Teredo's habitat includes wood, wooden ships, piers, coconuts caught on the seabed and rhizomes of marine plants. These mollusks have perfect adaptations for drilling passages in wood. The wood borer covers its passage with calcareous secretions from the mantle, due to which a protective tube is formed. At the back of the body there are 2 thin long siphons that serve for inhalation and exhalation. These siphons can be significantly extended from the passage, with their help the mollusk communicates with the external environment, mainly for feeding and respiration.
By observing how many pairs of siphons stick out from holes in the wood, you can determine how many shipworms are doing destructive work here. In the back of the mollusk’s body there are not only siphons, but also peculiar chitinous plates. When the shipworm exposes the siphons from the hole, it pulls the plates inside. If the mollusk is in danger, it draws siphons into itself and closes the hole with chitinous plates. Over time, the stroke expands deeper, and the hole is so small that the plates can easily close it.
A small but strong shell is found only in the front part of the mollusk. U adult the shell makes up approximately 1/40 of the entire body length. In front, between widely spaced shells, there is a small rounded leg, and behind there is a soft, elongated body.
The mollusk uses shell valves to drill into wood. The front end of the shell protrudes in front, it looks like an ear with horizontal thin notches. Middle part covered with stronger ridges with large teeth. These ridges are placed at right angles to the ridges located in the front part. The back of the shell of the mollusk is smooth. The shipworm, pushing the doors apart and moving, rubs its combs along the wood, forming a passage in it, like a drill. Woodworms make drilling movements 8-12 times per minute.
It is noteworthy that the passages of different individuals never intersect with each other, no matter how a large number of There were no woodworms in the infested wood. Most likely, the shipworms hear drilling sounds from the neighboring passage, turning their course, thanks to this the neighbors do not collide with each other. Because of such bends, the wood suffers even more; mollusks practically riddled it.
How do shipworms feed?
Like all molluscs, teredos feed by filtering marine plankton. The shipworm sucks water and sawdust collected during drilling through the inlet siphon.
Since wood is very difficult to digest, the mollusk’s stomach has a blind, pouch-like outgrowth big size, it is always filled with sawdust. The woodborer scrapes off pieces of wood with its shell, then they fall into the mouth, and then into the stomach. In the stomach, sawdust is absorbed by amebocytes, digestion occurs intracellularly. Shipworms are members of a small group of creatures that can use a special enzyme to break down cellulose and convert it into glucose. These enzymes are present only in some flagellates and ciliates.
Reproduction of shipworms
Teredos are bisexual organisms, meaning each individual is capable of producing both sperm and eggs. Sperm are formed first, and then eggs, which prevents self-fertilization. In some cases, eggs are formed without fertilization.
Shipworms are bisexual creatures. Fertilized eggs are first formed in the gill cavity, and after 20-30 hours they become larvae, and after another 36-48 hours a veliger larva is obtained. After only 2-3 weeks, the veliger enters the water, in which it floats with the help of a sail for 2-2.5 weeks. The veliger of the shipworm has the same appearance as that of other mollusks. After the veliger finds a piece of wood, it attaches itself to it using a byssus. At this time, the woodworm is still similar to an ordinary bivalve mollusk: its shell is normally developed, it covers the entire body, there is a long leg in front, and short siphons in the back. A byssus emerges from the leg, which is used to attach the veliger to the wood. During further development The veliger turns into a “worm” that has no external resemblance to traditional mollusks.
Measures to combat shipworms
The result of the “work” of a ship worm. Woodworms are dangerous pests of docks, pilings and wooden ships. In past centuries, when wood was the main material for shipbuilding, shipworms were terrible enemies of the fleet; they destroyed wood, resulting in the destruction of the sides of ships.
Shipworms are widespread, they live in almost all seas, they are not found only in the icy Arctic waters. Teredo navalis lives in the Baltic and Black Seas, whose body length reaches 25 centimeters, and in the Barents Sea lives even more major representative species - T. megotara. Several small species of wood borers live in the Far Eastern seas.
Measures to combat these wood pests are quite varied, but most often paints and varnishes with toxic substances are used to coat wooden structures. Coal varnish, creosote and carbolic acid are mainly used.
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The animal called the giant shipworm is actually bivalve mollusk. Molluscs from the family Teredinidae are known as "ship worms", and the definition of "ship" was inherited by K. polythalamia. Let us explain that relatives K. polythamia They feed, among other things, on the remains of sunken wooden ships - wood.
The habitat of the animals remained unknown to scientists.
But a case helped here: one of the members of the research group studied documentary, aired on Philippine television, and then shared it with colleagues. The video demonstrated strange creatures, which were planted (like carrots in beds) in the mud of a shallow lagoon. After watching the film, scientists organized an expedition and found living specimens for the first time K. polythalamia.
After the live shipworm finally fell into the hands of scientists, the entire group of researchers literally crowded around Distel. The researcher carefully washed the sticky dirt from the outside of the creature's "shell" and then carefully pulled it out of the top hole (in fact, the whole process is shown in the video below).
“I was amazed when I first saw the size of this strange animal,” says University of the Philippines researcher Marvin Altamia. 
Due to the fact that the animal has never been thoroughly studied before, today experts know little about its lifestyle, habitat and other important details. "We suspected that giant shipworms were fundamentally different from wood-eating shipworms. And the discovery of the animal confirmed this," said senior study author Margo Haygood of the College of Pharmacology at the University of Utah.
Experts say they were faced with a difficult dilemma: they had to understand why K. polythalamia so different from other similar creatures. And the answer may lie in the remote habitat where the valuable specimen was found. It is noted that the lagoon is filled with rotting wood. 
It is noteworthy that common shipworms burrow deep into wood washed out into the ocean. Animals chew and digest it with the help of bacteria. Unlike their relatives, K. polythalamia lives in dirt, but it also turns to bacteria to get food. True, he does it in a different way.
Researchers say that K. polythalamia lives in a rather bad-smelling place: rich organic substances the dirt that is present around the creature's home emits hydrogen sulfide. This gas, obtained from sulfur, has a distinct odor that can be compared to the “aroma” of rotten eggs. Such an environment may be harmful for humans, but for giant worms it is just right, scientists say. 
Experts note that the worms themselves do not eat, or they eat, but very, very little. Instead, they rely on beneficial bacteria living in their gills. They are the ones who produce food for K. polythalamia. These tiny "cooks" use hydrogen sulfide as energy to produce organic carbon, which feeds the shipworms. This process is similar to that characteristic of plants: they use the energy of the sun to transform carbon dioxide in the air into simple carbon compounds during photosynthesis.
Researchers note that as a result of this method of nutrition, many organs of the digestive system K. polythalamia simply decreased as unnecessary.
Lifestyle unusual creatures is consistent with the hypothesis that Distel proposed two decades ago. Receipt various types beneficial bacteria may explain how shipworms evolved from wood-eating organisms to using poisonous gas in the mud to survive.
Scientists intend to further study the role wood played in the unique transition from ordinary shipworms to giant ones. "We're also interested in finding similar transitions that other animals that live in unique places all over the world,” adds Distel.
The results of the study were published in the scientific publication Proceedings of the National Academy of Sciences.
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