Which are called "ship worms". No, we were not mistaken - such animals really exist.
Ship worm: class and type of animals
The thing is that the ship worm, which is also called teredo, or woodworm, has undergone significant changes in the course of evolution. They especially concern the external structure of the animal. Therefore, at first glance, it is quite difficult to figure out which class the ship worm belongs to. In fact, this is the 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 molluscs, it has inherent structural features. Where is his sink? It is located at the front end of the body and consists of two small valves about 1 cm in size. With their help, the mollusk drills wood. Each flap is formed by three serrated-edged parts.
Otherwise, the shipworm mollusk has structural features typical for this systematic unit. Its body is flattened from the sides and consists of two sections: the trunk and legs. Since they do not have a head, they also lack the organs located on it. pharynx, grated tongue, jaw and salivary glands. The robe covers the back of their body. There are also glands that secrete calcareous substances.
Almost the entire body of a ship worm is in wood. On the surface, it leaves only the rear end with a pair of siphons. Through them, the relationship of the animal with the environment is carried out. The protection mechanism teredo is also interesting. Along with siphons, at the posterior end of the body there is a plate of solid carbon 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 bivalve molluscs live in water. They can be found in all seas, except for the coldest ones. This is due to the fact that they feed by filtration. The ship's worm passes water through the siphons with organic residues that are in it. Another teredo is wood. With the help of a reduced shell, they make moves in it. Therefore, they often live in the wood of piers and ships, snags that have fallen to the bottom, and rhizomes of marine plants.
Internal structure
Like all molluscs, shipworms have a secondary body cavity. However, the gaps between the organs are filled with loose connective tissue. The circulatory system of these animals is open. 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 takes place. Blood flows to the heart through the veins. The ship worm is a cold-blooded animal. Therefore, he cannot live in very cold water.
The respiratory organs of the woodworm are the gills, with the help of which it absorbs oxygen from the water. The excretory system is represented by the kidneys. They excrete metabolic products into the near-mantle cavity. The ship worm has a scattered-nodular nervous system.
Features of life
The ship worms are in constant action. They make about ten drilling movements per minute. At the same time, they move apart the doors, which destroy the wood with their notches. The size of the passages of the ship worm increases with the growth of the animal itself. They can reach 2 meters in length with a diameter of 5 cm. Another name for them is associated with this way of life - woodworms. It is surprising that the passages of these molluscs never intersect. Scientists assume that they hear the approaching sounds of the "neighbor" drilling and change their direction. This is the respect animals show to each other!
Certain enzymes are required to digest the complex carbohydrate of cellulose that makes up wood. Teredo are unable to produce them on their own. A feature of the structure of their digestive system is the presence of a long blind outgrowth of the stomach, in which sawdust constantly accumulates. Symbiotic bacteria live here. They also break down cellulose to glucose monosaccharide. Another function of symbionts is to fix nitrogen in water.
Reproduction and development
Shipworms are hermaphrodites. This means that one individual forms both male and female reproductive cells. Fertilized eggs are first found in the branchial cavity, in which they develop for up to 3 weeks. Their larvae develop. They go out into the water and swim here for 2 more weeks. The leg of the mollusk begins to secrete a special protein substance in the form of a thread - bisus. With its help, the larva is attached to the wood. During this period teredo has the typical appearance of a bivalve mollusk. Most of its body is hidden by shells, from which a leg protrudes noticeably. As the animal develops, it becomes like a worm.
Significance in nature and human life
The shipworms have rightfully earned a bad name. They really do a lot of harm by 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. Ship worms are capable of completely destroying the bottom or sides of the ship, turning the supports of bridges and marinas into dust, and causing the death of sea plants. Now wood, which can become a "victim" of ship worms, is coated with special toxic substances that make it "inedible" for these molluscs.
So, shipworms, despite their name, are representatives of the class "Bivalve molluscs". 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, which have undergone a troupe of mollusks called shipworms, or woodworms, are so profound that many of them have lost their original appearance of bivalve molluscs.
Such is the shipworm (Teredo), which is actually, of course, not a worm, but a mollusc. He got the name of the worm for its long, naked body. A small shell of a peculiar structure plays the role of a drill and is located at the front end of the body.
The structure of the ship worm
The structure of a ship worm is a vivid example of adaptation to changed living conditions. Pieces of wood, pier piles, wooden boats, rhizomes of sea plants and even coconuts sunk in the sea are common habitats. Ship worms have the most sophisticated adaptations for grinding through wood. The mollusk, drilled in the tree, covers the mantle with lime secretions, as a result of which a protective tube is formed. At the posterior end of the body, there are two long, thin siphons - inhalation and exhalation. They can be strongly pulled out of the passage and serve to connect the mollusk with the external environment: primarily for respiration and nutrition.
By counting the number of pairs of siphons sticking out of small holes in the wood, you can determine how many individuals are often doing destructive work in a given place. In addition to siphons, there are peculiar chitinous plates at the posterior end of the body. When the siphons are pushed out of the travel bore, the plates are pulled inward. At the slightest danger, the mollusk draws in the siphons, and plugs the opening of the passage with chitinous plates. The stroke gradually widens inward from the inlet, and the hole itself is so small that the plates easily close it.
A small, sturdy shell covers only the anterior end of the mollusc's body. In an adult carpenter moth, the shell occupies only 1 / 30-1 / 40 of the body length. A small rounded leg protrudes from the front between the widely spaced shell valves, and an elongated soft body behind.
Sink shutters are an excellent tool for drilling wood. The anterior part of the shell projects forward in the form of an abalone with horizontal finely serrated ridges. The middle part is covered with powerful ridges with coarser teeth. These ridges are at right angles to the front ridges. The back of the shell is smooth. Moving and pushing the shutters, the mollusk rubs the wood with its combs and grinds through the course like a drill. Drilling movements teredo produces rhythmically 8-12 times per minute. It is interesting that the neighboring passages of carpenter borers never intersect, no matter how densely they pass in the wood they infected. Apparently, the worms somehow perceive the drilling sounds coming from the adjacent move, and make turns of their move so as not to collide with the neighbor. Such bends in the passages lead to even more ridging of the wood.
How ship worms eat
As befits bivalve molluscs, shipworms feed by filtration on marine plankton, sucking water through an inlet siphon, as well as sawdust, which is scraped off during drilling.
Due to the diet of wood, which is very difficult to digest, the stomach teredo has a large blind saccular outgrowth, always filled with sawdust. Pieces of wood scraped off by the shell are swallowed through the mouth and into the stomach. There they are absorbed by amoebocytes and digested intracellularly. The ship worm belongs to an extremely small group of animals that have an enzyme that breaks down cellulose into glucose. As you remember, some ciliates and flagellates have such enzymes.
Reproduction of ship worms
Shipworms are bisexual organisms, but each individual, passing to reproduction, first produces spermatozoa, 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, after another 36-48 hours - a veliger larva. 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 molluscs. Having found a piece of wood, he settles, attaching itself with a byssus. At this moment, the shipworm is still similar to an ordinary bivalve mollusk: its shell is normally developed and covers the whole body, a long leg protrudes forward, and short siphons slightly protrude from the shell behind. The leg is able to secrete byssus, with the help of which the veliger is fixed on the tree. Further development turns teredo into a "worm", unlike an ordinary mollusk.
Control measures against shipworms
Ship worms are dangerous pests of wooden piles, docks, and underwater parts of wooden ships. In past centuries, when all ships were built of wood, ship worms were terrible enemies of the fleet, completely exhausting the bottoms and sides of ships. Marine woodworms are very widespread and are found in almost all seas of both hemispheres, 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 ship worms also live in the Far Eastern seas.
Measures to combat ship woodworms are very diverse, but are mainly reduced to coating underwater wooden structures with varnishes, paints, impregnating wood with substances toxic to mollusks - creosote, coal varnish, carbolic acid.
Few of 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 kind of sea creature known as a ship worm or shashen (according to V. Dahl, "to be fiddled" means to tinker or fumble) ...
This animal could knock out a completely new ship in just two or three months, turning its wooden bottom literally into a sieve. But it wasn't just the fleet that suffered from the worm. Any tree immersed in water quickly fell into disrepair. But until the beginning of the 20th century, most of such marine structures as breakwaters, embankments and piers were made of wood. In 1731-1732. the shipworm, unexpectedly multiplying in unprecedented numbers off the coast of Holland, damaged the wooden piles of the dams, in connection with which two provinces of this country were under the threat of flooding.
It was then that the Dutch scientist Gottfried Zell, who, at the request of coastal residents, studied the shipworm, was the first to find out that this sea creature is not a worm at all, but a bivalve mollusk, whose shell has changed and turned into a device for drilling wood. Today, about 70 species of marine carpenter molluscs are known, which are widespread in the 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 mangrove thickets and woody remains carried into the sea by rivers. But as soon as a person began to master the marine environment, wood-boring mollusks began to settle in the underwater parts of wooden ships and various hydraulic structures, carving passages in them and thus destroying them.
Ship worms have adapted to a very peculiar way of life. The adults of these molluscs live in tunnels that are grinded into the wood with their modified shell. They have a worm-shaped cylindrical body up to 0.5-1.5 m long (hence the name ship worm), 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 cover a small entrance hole when the animal is drilling wood. At the front end there is a relatively small (up to 1 cm), but very strong bivalve shell with notches, which is an excellent tool for drilling wood. During this process, the mollusk attaches itself to the wall of the passage with the help of its legs, opens the flaps and makes rhythmic movements with them (from 8 to 12 times a minute), in which they, like a rasp, rip off a layer of wood. The walls of the passage are lined by the mollusk from the inside with a thin layer of lime deposits. It is interesting to note that, no matter how densely the shipworms populate the wood, their passages never intersect, so a heavily affected piece of wood resembles a honeycomb in cross section. Since shipworms penetrate wood in the larval stage, their entry holes are microscopic and subtle. Therefore, it often turns out that the wood is completely riddled, although at first glance it looks completely intact. The course of a shipworm increases as it grows and can reach 2 m in length and 5 cm in diameter.
These mollusks feed on organic residues and small plankton, which are filtered out of the water sucked in through siphons, and also by processing sawdust formed during drilling. Shipworms are hermaphrodites (i.e., periodically function as males or females) and are very fertile. Three to four times a year, they produce from 1 to 5 million eggs, which for about two weeks develop in the branchial chamber of the animal that gave birth to them. The larvae that emerged 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 to it with byssus threads. Immediately, after quickly transforming into a tiny and seemingly very ordinary bivalve mollusk, young individuals of shipworms begin to scrape the tree with the sharp edges of the shell. Having scraped together a small pile of sawdust, they cover themselves with them, like a hut. Protected in this way, young mollusks change their appearance unrecognizably in a few days - their body narrows and takes on a worm-like shape, like that of their parents. After that, they invade the tree and begin the life of a ship worm. The juveniles grow rapidly and within three months become capable of producing offspring.
Since shipworms have caused enormous damage to shipping and various hydraulic structures for a long time, people are constantly looking for effective means of combating them. In addition to covering the bottoms with special poisonous paints, for many years the regular entry of wooden ships into rivers was widely practiced (drying within a month gave a good effect), especially during the breeding season of ship worms and settling of their larvae, which are very sensitive to desalination. In the end, although this made the ships more expensive and heavier, the shipowners began to sheathe their bottoms with lead and copper sheets, for no tree could withstand the drilling force of the worms' doors. But all this was of little use until poisonous chemical impregnations for wood (first of all, creosote) were invented, then they completely switched to steel shipbuilding.
Although shipworms usually avoid coastal waters with low salinity, since the early 1990s, the shipworms began to actively settle along the Danish and German coasts of the Baltic Sea. In recent years, there has been a threat of its penetration into the coastal area of Sweden. Scientists believe that the expansion of the geographic range of this shipworm is due to climate change, that is, an increase in water temperature helps the mollusk to adapt to conditions of low 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 undisturbed only because the shashen 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 sunken ships of archaeological value. Despite all this, it should not be forgotten that carpenter molluscs play an important role in processing any wood that ends up in the sea.
Their waste products and they themselves become food items for various marine organisms. Some species of ship worms in the countries of Southeast Asia are specially bred for use in food, because they are the same shellfish as oysters and mussels.
Ship worms or woodworms belonging to the family of molluscs have undergone such changes in the process of evolution that they have completely lost their external resemblance to bivalve molluscs.
In fact, the shipworm Teredo is not a worm, it is a shellfish. The mollusk began to be called a worm for its long body.
A small shell is located at the front end of the body and serves as a drill.
The structure of the ship worm
In connection with the changing living conditions, the structure of the ship worm has also changed. The habitat is often timber, wooden boats, marinas, coconuts found on the seabed and rhizomes of marine plants. These molluscs have perfect adaptations for drilling into the wood of the holes. The carpenter covers the completed course with calcareous secretions of 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 pulled out of the passage, with their help the mollusk binds to the external environment, mainly for nutrition and respiration.
By observing how many pairs of siphons are sticking out of holes in the wood, you can determine how many shipworms are doing destructive work here. In the back of the body of the mollusk there are not only siphons, but also peculiar chitinous plates. When the shipworm pushes the siphons out of the hole, it pulls the plates inward. If the mollusk is in danger, it draws in the siphons, and closes the hole with the help of chitinous plates. Over time, the stroke expands inward, and the hole is so small that the plates can easily close it.
A small but sturdy shell, present only in the anterior part of the mollusk. In an adult, the shell is about 1/40 of the entire body length. In front, between widely spaced shells, there is a small rounded leg, and in the back there is an elongated soft body.
The shells are used for drilling wood. The anterior end of the shell protrudes in front; it looks like an abalone with horizontal thin notches. The middle part is covered with stronger ridges with large teeth. These ridges are placed at right angles to the front ridges. The back of the shell in the mollusk is smooth. The ship's worm, pushing and sliding the flaps, rubs its ridges on the wood, forming a course in it, like a drill. Wood borers perform drilling movements 8-12 times per minute.
It is noteworthy that the passages of different individuals never intersect with each other, no matter how many woodworms are in the infected wood. Most likely, shipworms hear boring sounds from the adjacent passage, turning their course, thanks to this, the neighbors do not collide with each other. Due to such bends, the wood suffers even more, mollusks practically riddled it.
How ship worms eat
Like all molluscs, they feed heavily by filtering out marine plankton. The ship's worm sucks in water and sawdust accumulated during drilling through the inlet siphon.
Since wood is very difficult to digest, the stomach of the mollusk has a large blind saccular outgrowth, it is always full of sawdust. Woodworm scrapes pieces of wood with a shell, then they fall into the mouth, and then into the stomach. In the stomach, sawdust is absorbed by amoebocytes, digestion occurs intracellularly. Shipworms are representatives of a small group of creatures that can, using a special enzyme, break down cellulose and convert it into glucose. These enzymes are found only in some flagellates and ciliates.
Reproduction of ship worms
Teredo are bisexual organisms, that is, each individual is capable of producing both sperm and eggs. First, sperm are formed, and only then eggs, thanks to this, self-fertilization is excluded. In some cases, eggs are produced without fertilization.
Shipworms are bisexual creatures. Fertilized eggs first form in the gill cavity, and after 20-30 hours larvae are obtained from them, 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 a sail for 2-2.5 weeks. The shipworm veliger has the same appearance as the rest of the molluscs. After the veliger finds a piece of wood, it is attached to it with a byssus. At this time, the woodworm is still similar to the ordinary bivalve mollusk: its shell is normally developed, it covers the whole body, there is a long leg in front, and there are short siphons in the back. A byssus stands out from the leg, which is used to fasten the veliger to the wood. During further development, the veliger turns into a "worm" that has no external resemblance to traditional mollusks.
Control measures against shipworms
The result of the "work" of the ship worm. Woodworms are dangerous pests of marinas, piles and wooden ships. In past centuries, when wood was the main material for shipbuilding, shipworms were terrible enemies of the fleet, they destroyed wood, as a result of which the sides of ships were destroyed.
Ship worms are widespread, they inhabit almost all seas, they are not found only in the icy Arctic waters. Teredo navalis lives in the Baltic and Black Sea, the body length of which reaches 25 centimeters, and an even larger representative of the species, T. megotara, lives in the Barents Sea. Several small species of woodworm live in the Far Eastern seas.
Measures to combat these pests of wood are quite diverse, but paints and varnishes with toxic substances that are used to cover wooden structures are most often used. Coal varnish, creosote and carbolic acid are mainly used.
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The animal called the giant shipworm is actually a bivalve mollusc. Molluscs from the family Teredinidae known as "shipworms", and the definition of "shipworm" was inherited and K. polythalamia... Let us explain that relatives K. polythamia feed, among other things, the remains of sunken wooden ships - wood.
The habitat of the animals remained unknown to scientists.
But chance helped here: one of the research team members studied a documentary aired on Philippine television and then shared it with colleagues. The video showed strange creatures that were planted (like carrots in beds) in the mud of a shallow lagoon. After watching the film, scientists organized an expedition and found live samples for the first time. K. polythalamia.
After the living shipworm finally fell into the hands of scientists, the entire group of researchers literally crowded around Distel. The researcher thoroughly washed the sticky dirt from the outside of the "shell" of the creature, and then carefully pulled it out of the upper hole (in fact, the whole process is shown below in the video).
"I was amazed to see the size of this strange animal for the first time," 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 assumed that giant shipworms were fundamentally different from wood-eating shipworms. And the animal's discovery confirmed this," said senior study author Margo Haygood of the University of Utah's College of Pharmacology.
Experts say they were faced with a difficult dilemma: they needed to understand why K. polythalamia so different from other similar creatures. And the answer may be hiding in a remote habitat in which a valuable specimen was found. It is noted that the lagoon is filled with rotting wood. 
It is noteworthy that ordinary shipworms burrow deep in the wood carried out into the ocean. Animals chew and digest it with bacteria. Unlike their relatives, K. polythalamia lives in mud, but it also turns to bacteria for food. True, he does it in a different way.
Researchers say that K. polythalamia lives in a rather foul-smelling place: the dirt rich in organic matter that is present around the creature's dwelling emits hydrogen sulfide. Derived from sulfur, this gas has a pronounced odor that can be compared to the "aroma" of rotten eggs. Such an environment can be harmful to humans, but that's what the scientists say for giant worms. 
Experts note that the worms themselves do not eat, or they do, 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 "chefs" use hydrogen sulfide as energy to produce organic carbon, which feeds the ship's worms. This process is similar to that of plants: they use energy from the sun to convert carbon dioxide in the air into simple carbon compounds during photosynthesis.
The researchers note that as a result of this method of nutrition, many organs of the digestive system K. polythalamia simply decreased as unnecessary.
The lifestyle of unusual creatures is consistent with the hypothesis that Distel proposed two decades ago. Obtaining different types of beneficial bacteria may explain how shipworms evolved from wood-eating organisms to using poisonous gas in the mud in order to survive.
Scientists intend to further study the role of wood, which it played in the unique transition from ordinary shipworms to giant ones. “We're also interested in looking for similar transitions that other animals in unique locations around the world might have,” adds Distel.
The research results are published in the scientific journal Proceedings of the National Academy of Sciences.
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