Teredo Navalis is a wood-boring mollusk classified in the group of saltwater clams. It is a soft-bodied invertebrate with a small shell with two hinged parts at its anterior end. Teredo Navalis is also called Naval Shipworm or Turu. It is because T. navalis is known for attacking and devouring the wood of the ships. It is capable of wreaking havoc on any wood they consume.
Teredo Navalis has gotten the name “worm” because of its distinctively worm-like appearance. Unlike the other Bivalvia, whose bodies are encased inside their shells, shipworms have reduced shells only around their anterior part. The rest of their body is naked, allowing them to bore into the wood.
Teredo Navalis can also be called the beast of the sea because it has plagued sailors by damaging their ships. Teredo Navalis has many interesting and unusual features. So, let’s explore more about this bizarre beast below in our article.
About Teredo Navalis – A Quick Biology
Following is the summary of some key biological information concerning Teredo Navalis:
|Scientific name||Teredo Navalis|
|Diet||Wood, dust and debris|
|Size||1.5cm to 58cm long|
Description of Teredo Navalis
Teredo Navalis has a long and thin worm-like body with tapered ends. The head and tail regions of the shipworms cannot be identified. However, the anterior end can be marked by two hinged shells. These shells are white in color, each having three triangular lobes. This shell of T. navalis is the only most obvious clam-like part of its body.
Although the primary purpose of shells in the phylum of mollusks is to provide protection, the shells of shipworms help them tunnel through the wood. Thus, the protective role of the shell is no longer served. The body of the teredo Navalis is thickened and muscular at the anterior end.
Taxonomy of Teredo Navalis
According to the taxonomic classification of Teredo Navalis, it belongs to the phylum Mollusca because of its anatomy and morphology of mollusks. Within the phylum Mollusca, Teredo Navalis is placed in the class of Bivalves due to the presence of a shell with two valves.
All the bivalve clams, including Teredo Navalis, are then classified in the order Myida. Among these clams of Myida, all those species of saltwater clams notorious for burrowing into the wood are categorized in the taxonomic family named Teredinidae. This family of mollusks comprises 16 different genera of wood-drilling shipworms.
Teredo is a genus among these 16 genera of shipworms. This genus comprises 13 species of highly modified wood-drilling shipworms and T. navalis is one among them.
Physical Characteristics of Teredo Navalis
Teredo Navalis has a cylindrical, elongated, and reddish worm-resembling naked body. Despite having a worm-like appearance, T. navalis has all the characteristics of a mollusk. Naval shipworms can grow up to 1.5 cm to 58 cm. The shell at the anterior end only covers about 2 cm of its body.
The shell of Teredo Navalis is composed of calcium carbonate. This shell is also covered with the lining of light brown periostracum, an organic material coating. The shell also has sharp ridges and rasp-like denticles that help the shipworms to burrow in the wood. The shell can be divided into three distinct lobes or regions.
The mantle of the Teredo Navalis extrudes calcareous secretions that line the insides of the tunnel Teredo has made in the wood. Thus, the tubes and tunnels made by the naval shipworms are always covered with calcareous linings. The anterior end of the shipworm is always buried inside the tunnel, while the posterior end protrudes out from the tunnel’s opening.
The posterior ends of shipworms have two siphons, called inhalant and exhalant siphons. The inhalant or incurrent siphon is used for filter feeding, sperm reception, and respiration.
In contrast, exhalant or excurrent siphons are used for excretion and sperm release. In the situation of a threat, naval shipworms draw back their siphons and cover the opening of the tunnel with a calcareous pallet.
Behavior of Teredo Navalis
The adult shipworms are attached to a substratum, mainly wood. They are sedentary organisms and show no motility during their life. However, during the larval stage, naval shipworms are fairly free-swimmers. Veligers, the developed larvae of shipworms, swim through the water to find a suitable wooden substrate.
After the attachment, the free-swimming young larvae undergo an extensive metamorphosis. Metamorphosis is a biological transformation of an organism from one body form into a distinctively different one. After the metamorphosis, the larval shipworm attains its adult worm-like appearance.
The adult shipworm spends its entire life attached to the same substratum. As it feeds, it keeps growing in size. Simultaneously, it keeps digging in the wood to accommodate its increasing length.
The intersection of the two tunnels present in the same substratum never happens. It is because T. navalis can sense other burrows in its vicinity. Thus, it drills in different directions to avoid overlapping.
Habitat, Range, and Distribution
Although the naval shipworm has been destroying the ships of sailors for decades, the origin of the Teredo Navalis is still a mystery. However, T. navalis is found explicitly in temperate oceans and seas.
It is abundantly found in the Baltic Sea, Pacific Oceans, and Atlantic Oceans. The naval shipworm has a widespread distribution all around the world.
The adult naval shipworms inhabit different wooden structures submerged in the water. Teredo Navalis can be found tunneling the pieces of driftwood, timber, pillings, wooden vessels, hardwood, hulls of ships, floating wood, wooden wharves, or any other available wooden substrate. Teredo Navalis bores into the wood and leaves it riddled with tunnels and holes.
Naval shipworms are widespread due to the immense distribution of this organism through the ships. When an infested ship travels from one part of the world to another, it also transports the shipworms.
Thus, shipworms are introduced to new locations they have not exploited before. This way, the naval shipworms spread and established their species in new places.
Diet and Digestion of Teredo Navalis
Teredo Navalis Chifley feeds on the wood and cellulose obtained from it. But it is also a filter feeder. This means naval shipworms feed on small particles, dust/debris, zooplankton and phytoplankton. This feeding occurs through their incurrent siphons protruding out from their burrows.
In naval shipworms, the process of digestion occurs unusually. Although they are wood-consuming organisms, their stomach cannot produce the cellulase enzyme to digest the cellulose.
Naval shipworms have a tight symbiotic relationship with microbes that can secrete wood-digesting enzymes. These microbes live in a specialized pouch present in the gills of shipworms.
Shipworms actually eat the wood they excavate to create the tubes they inhabit. The bits of wood they scrape off with their shells are carried to their mouth by cilia on their body.
These wood shavings travel to a specialized structure in their gut. Here, symbiotic bacteria contribute to the process of digestion. The digestive enzymes secreted by the microbes travel to the gut for the digestion process.
Life Cycle and Reproduction System
The life of a naval shipworm starts as an embryo in the gill chamber of the female parent. The embryo grows and develops in the gill chamber, then undergoes metamorphosis to become a free-swimming larva. These larvae are then released into the water and are known as veligers.
Veligers then develop velum, an organ that helps them move and feed. A shell also appears on the bodies of these free-swimming larvae. These larvae find a suitable wood substratum to feed on.
Once these larvae attach to a wooden structure, they again undergo the process of metamorphosis to become adult clams. The occurrence of metamorphosis marks the life cycle of Teredo Navalis.
The reproductive cycle of T. navalis is another unusual physiological process like digestion. They undergo sex alteration during their lifetime. The naval shipworms are male first.
But they transform into female adults later in their life cycle. Adult shipworms can be anything at any time. They can possess eggs and sperm simultaneously. But they also can switch between having either sperm or eggs.
Naval shipworms have different mechanisms for sexual reproduction. During the warmer months of the year, the adults release their eggs and sperm in the water. This is called broadcast spawning.
Another way of reproduction found in naval shipworms is internal fertilization. In this process, female shipworms collect free-floating sperm from the water to fertilize their eggs internally.
Cardiovascular and Nervous Systems
Being a bivalve mollusk, Teredo Navalis has an open blood circulatory system. This means that blood in its body directly bathes all of its organs.
The heart of naval shipworm has three chambers which two chambers are atria and one chamber is the ventricle. The atria receive oxygenated blood from the gills. Ventricle plays the role of pumping the blood in the body.
Teredo Navalis has a very basic and primary nervous system because of its stationary lifestyle. Naval shipworms do not have properly developed brains. Instead, they have plexus of nerve ganglion at the anterior ends of their bodies. They have paired nerves running along the length of their bodies.
Naval shipworms also have developed senses and sensory organs. Their sensory organs help them in chemotaxis and identification of nearby tunnels in the wood. The siphons of Teredo Navalis are also vibration-sensitive. Therefore, in the case of a threat, they get drawn back into the tunnel.
Despite being destructive to important wooden structures, Teredo Navalis also plays a significant ecological role in sea life. These clams fill an important ocean niche. Naval shipworms are the recyclers of the ocean.
These clams biodegrade all the harmful submerged woody material in the ocean. In this way, shipworms protect the ocean from pollution and also protect the habitat of other small living organisms. They also recycle the carbon trapped in the wood by digestion of the cellulose of the wood.
Naval shipworms also provide habitats by boring long tunnels in different wooden structures. These tunnels and holes can be used by other mollusks, zooplankton, and crustaceans as living space. Living in these tunnels will also protect the small creatures from predation.
Relationship with Humans
Teredo Navalis had been the cause of the destruction of important wooden structures made by humans for decades. This means the naval shipworms have a long record of bad relationships with humans. In the past, the shipworms have also been the cause of the destruction and wrecking of the ships of Cristopher Columbus.
Shipworms have always been the bane of sailors since we first put the seas. Thus, humans have always been finding ways to protect their essential submerged wooden structures from the invasion of shipworms.
Teredo Navalis does not have any apparent health effects on humans. Therefore, it is also eaten as a delicacy in different parts of the world.
What is Teredo in biology?
Teredo Navalis is a bivalve mollusk that has a prominent appearance of a worm. It belongs to the group of saltwater clams that are classified in the family Teredinidae because of their wood-drilling nature.
Teredo Navalis is also termed as the termites of the seas. It is because this mundane sea creature leaves the wood extremely perforated after inhabiting it.
This invasive sea beast cannot digest the cellulose of the wood itself. Thus, it has an important symbiotic relationship with other wood-digesting microorganisms. In this mutually beneficial relationship, the bacteria inside the shipworm use the wood’s H2S as an energy source and give the shipworm cellulose in exchange.
How to prevent Teredo Navalis mollusks?
Humans have been trying to find methods to prevent the attack of Teredo Navalis on their wooden structures that are submerged in water. These structures include ships, piers, wharves, and docks. Following are the methods that can be followed to prevent Teredo Navalis:
Coatings: We can apply different adhesive coatings on the wood that may prevent shipworms from invading it. The wooden structures coated with paints and other coatings are less susceptible to the attack of shipworms.
Treating: We can also treat the wooden structures with copper, iron, biocides and other chemicals. This will make the wood inaccessible to the shipworms.
Nod-wood material: We can use materials other than wood to build structures submerged in water for long periods. This is because shipworms cannot exploit all materials other than wood.
Are Teredo Navalis Endangered?
No, the species of Teredo Navalis is not endangered. It is because naval shipworms reproduce on a large scale through spawning. Moreover, adult shipworms are not at risk of predation because they remain hidden inside wooden constructions.
Also, IUCN has not yet evaluated the conservatory status of Teredo Navalis. Therefore, it is difficult to predict whether or not naval shipworms are endangered.
Effects of Temperature, Salinity, and Substratum on Larvae of Teredo Navalis
The larvae of Teredo Navalis require optimal temperature, salinity, and availability of the substratum to grow and flourish. They can endure a slight change in temperature and salinity. But the extensive changes in the temperature, pH, and salinity of water can cease the development of the naval shipworms.
Salinity: Teredo Navalis can grow and sustain its life at a low salinity level. However, shipworms grow the best at high salinity levels. They reproduce and spread at a greater speed when there is a more than 12% salinity level.
Temperature: Teredo Navalis mostly inhabit the tropical and temperate temperature zones. This means that naval shipworms grow better at warmer temperatures. The temperature range that is most suitable for the reproduction of Teredo Navalis is from 15-30 degrees Celsius.
Substratum: The larvae need to find a suitable substratum right after a few days of its release. Water pollution with plastic and other pollutants can cause premature settlement and death of larvae.
Did you know the population status of Teredo Navalis?
The population of Teredo Navalis grows in a safe environment as they do not have any predators and remain protected in their wooden tunnels. Being wood-boring mollusks, shipworms also do not have any competition with other species for food. Naval shipworms reproduce and spawn when the temperature of the water increases and becomes warm.
This means that progressive climate change and global warming are accelerating the population spread of Teredo Navalis. As a result, it can be claimed that Teredo Navalis’ population status is conserved. But it’s also crucial to understand that maintaining and enhancing water quality is necessary to guarantee the survival of this population.
Why is Teredo Navalis called a shipworm?
Teredo Navalis is called a shipworm because it makes tunnels and perforations in the wood of the ships. These perforations cause the ships to sink. Shipworms are wood-drilling organisms and will attack anything made up of wood.
What does shipworm taste like?
Shipworms are edible and are eaten as a delicacy in different regions of the Philippines and Indonesia. Cooked shipworm usually tastes like all the other cooked clams. After cooking, the texture of shipworms becomes like cooked shellfish.
What’s the lifespan of Teredo Navalis?
The lifespan of Teredo Navalis is from 1 year to 3 years. Shipworms remain hidden in their tunnels. Therefore, they remain safe from the predation and attack of other different fishes.
Teredo Navalis has always been a bane to the sailors because it has caused many ships to sink. This tiny and mundane creature can turn big wooden structures into dust. Shipworms are actually the bizarre beasts of the sea. This worm-like creature is actually a mollusk with a soft and elongated body.
Teredo Navalis has also proved to be beneficial to the sea’s ecosystem. It degrades useless wooden structures and thus cleanses the sea from pollution. Teredo Navalis also recycles carbon and nitrogen fixation in the sea. These days, the warmer oceans due to climate change may give shipworms a boost in their population.