When we say the word worm, the first thing that comes in mind is a creepy, slimy, and a disgusting crawling creature. Worms look gross and ugly, but did you know that having worms in your soil is an indication of healthy soil? Well, this surprised us too!
Someone who does not know much about worms would think that worms are crawling creatures that live in the soil. However, some worms make living organisms like humans and animals their host to live. You read that right. Now that you have brought yourself here to get to know everything there is to know about worms, let’s start with the basics.
Table of Contents
- I. What Is A Worm?
- II. Types of Worms
- III. Common Parasite Worms That Cause Infection in Humans
- IV. Worm Infestation
- V. Earthworms-The Worm That Everybody Knows About
I. What Is A Worm?
A worm is a soft-bodied, elongated, invertebrate animal. Worms have long, cylindrical bodies that look more like a tube. Worms have no limbs. The size of worms varies vastly. Some worms are too small to be seen by the naked eye while some may be as big as 1 meter long. Worms may live in soil or water. However, there is a small variety of worms that occupy the category of parasites. Parasites are any organisms that live in the bodies of other living things (animals and humans).
The name worm originates from an old English word, wyrm. Most of the animals that are called worms are invertebrates. However, the term also encompasses amphibian caecilians and Anguis, the slow-worm which is a legless burrowing lizard.
Worms can be found anywhere. They can be found in soil, oceans, ponds, rivers, and even inside animals and humans. Since they are so abundant, it is important that you have sufficient knowledge about them.
II. Types of Worms
There are hundreds and thousands of types of worms that live in different habitats other than soil. However, the major groups in which different types of worms are divided into are as follows:
This group of worms includes tapeworms, flatworms, and flukes. Some of the worms in this group are parasites.
This group of worms includes roundworms, threadworms, and hookworms.
The worms that are included in this group are segmented worms like bristle worms and earthworms.
Platyhelminthes are the simplest animals that are bilaterally symmetrical. They are triphoblastic, which means they have three fundamental layers of cells. They are more commonly known as the flatworms. As the name indicates, flatworms have a flat body. Moreover, their bodies are soft and un-segmented. They do not have any body cavity except the gut. Smaller forms may even lack a gut. They do not have an anus as well. The ingestion and excretion of food, both are through the single pharyngeal opening. Despite having no cavity and a flat body, their gastro-vascular cavity is very well-developed.
Since their bodies do not have any cavity, the gut of larger flatworms is densely branched to ensure that food and nutrition are transported to all parts of the body. Owing to the fact that the flatworms have a flat body, and no cell is too far from the outside, they respire by the process of diffusion through the body surface. The excretory system of flatworms has protonephridia with the flame. A primitive nervous system is present.
Flatworms are hermaphrodites. Sexual reproduction takes place by fusion of gametes. In a few species of flatworms, asexual reproduction takes place through the process of regeneration and fission. The fertilization occurs within the body.
Most of the flatworms are parasites, with only a few types of worms in this group free-living.
Flatworms are further classified into three separate classes which are:
This class contains about 3000 species. Most of the flatworms in class Turbellaria are marine and benthic. Some may also be found in freshwater and in temperate and tropical terrestrial habitats.
All members of this class have dorso-ventrally compressed bodies with high surface area to volume ratios. The species that reside in marine habitats are colorful while terrestrial and interstitial species lack brightness. Locomotion in Turbellaria is with the help of cilia on a trail made with secreted mucus. Some species can also swim aided with rhythmic contractions of muscles. They are distinguished from other Platyhelminthes by the presence of a ciliated epidermis, sub-epidermal rhabdites, and free-living conditions.
Around 9000 species have been described under Trematoda. Most of the flatworms in this class are parasites that make vertebrates their host. Their bodies are covered with a tegument which is a peculiar epidermal arrangement. In this arrangement, the main bodies are relatively deeper and are separated by a muscle layer from the cytoplasm which lies next to the exterior. The main bodies are separated from the exterior but are also connected via cellular processes. The exterior layer is continuous.
Adult trematodes lack cilia. They have one to two suckers instead. They have a well-developed gut. Their reproductive, excretory, and muscular systems are relatively complete as well.
Cestodes are more commonly known as tapeworms. All cestodes are endo-parasites, needing at least two hosts. An adult cestode requires a vertebrate as its host. Many species of tapeworms inhabit humans.
They are different from flatworms due to a number of reasons. Unlike flatworms, the bodies of tapeworms are flat and long and are made from many segments that are called proglottids. Each segment is a separate reproductive unit, more likely a factory for gamete production. Adult tapeworms do not have cilia and the surface is covered with tegument as in trematodes. However, the tegument in cestodes is covered with microvilli that are tiny projections. The microvilli increase the surface area and thus, the cestodes can absorb nutrition from their hosts.
The digestive tract is completely absent in cestodes. Tapeworms have a specialized segment called the scolex at their anterior end which is covered with suckers or hooks that help the tapeworm to anchor to the host.
Nematodes are more commonly known as roundworms or human whipworms. They are extremely abundant. There are as many as 90,000 individual nematodes in one rotting apple. They have bilaterally symmetrical bodies that are surrounded by a flexible and strong non-cellular layer which is called a cuticle. The body plan of nematodes is simple. The epidermal cells secrete the cuticle which covers them. Muscle cells are present under the epidermal cells which run in a longitudinal direction.
Nematodes lack a true coelom. They have a pseudocoel instead. This pseudocoel is formed from the cavity of blastula directly rather than from folding or division of mesoderm. The cavity is small and filled with oviducts or testes, and an intestine mostly. They possess a simple nervous system with a ring of nervous tissue present around the pharynx. This gives rise to ventral and dorsal nerve cords that run through the length of the body.
Nematodes do not possess any cilia or flagella. The locomotion of nematodes is by the contraction of the longitudinal muscles. The internal pressure of their body is high which causes their body to flex and not flatten. As a result, they move by thrashing back and forth.
There are specialized cells for excretion of nitrogenous wastes in some nematodes while in others, canal alone, or canals with these specialized cells are present. They do not have flame cells.
Many species of nematodes are free living. They play significant ecological roles as predators on microorganisms and as decomposers. Some nematodes are parasites that affect humans directly and at times, indirectly (through domestic animals). Parasitic nematodes include roundworms (Trichuris trichiura), hookworms, pinworms, and filarial worms. They cause common infections in humans such as roundworm infection, filariasis, and onchocerciasis (river blindness), and trichuriasis.
Nematodes are divided into three major classes which are:
Class Rhabditea includes free-living as well as parasitic species. However, most of the parasitic nematodes are found in class Rhabditea. Most of the members of this class are un-segmented. They have cylindrical bodies that are tapered at one end. They possess a cuticle and a hyperdermis. Members of class Rhabditea have an inner and outer tube. The inner tube in adult species consists of a pharynx, gonads, and the intestine. They also have amphids which are invaginated cuticles with nerves.
They are two subclasses of class Rhabditea which are:
Members of this subclass are characterized by well-developed Plasmids which are posterior sensory structures. Their amphids are poorly developed
Members of this subclass are parasitic which are most often found in plants
Members of class Rhabditea have a chemically impermeable cuticle. This enables these worms to survive in extreme conditions and thrives as parasites. They also have a modified pharynx that allows these worms to have a compact body design as compared to members of class Enoplea.
Parasitic rhabdite includes human pinworm, Wuchererua species, and Necotar species which can cause a number of diseases which can be minor or severe. Examples of free-living nematodes in this class are members of the genus Caenorhabditis.
Members of class Enoplea have ancestrally diverged. They are a group of nematodes that is more ancestral which, unlike other nematodes, have not diverged much. Some worms that belong to class Enoplea are Diotphyme and Trichuris.
Enolpeans have cylindrical bodies. However, in some species, the esophagus is bottle-shaped. They have well-developed amphids that resemble a pocket. The pocket-like amphids of Enopleans can help distinguish them from the members of class Chromadorea. They also have a smooth appearance or they may have fine lines on their surface. Their excretory system is simple. It lacks lateral canals. Enolpeans lack plasmids.
Some members of class Enoplea are plant parasites such as members of order Dorylamida. Free-living nematodes of class Enoplea can be found in terrestrial and freshwater environments.
There are two subclasses of class Enoplea which are:
The members in this subclass have oval-shaped or a pouch like amphids, a smooth body, and cylindrical esophagus. Members of orders Enoplida and Trefusiida are included in this subclass.
Members of subclass Dorylaimia are found in freshwater and terrestrial environments. Majority of species are free-living nematodes. They exist either as omnivorous or predators in their respective environments. Only a few of its members, like Trichinellida are found as parasites.
Chromadorea consists of one subclass which is further divided into many orders. The members of this class have three esophageal glands, annules, and spiral amphids. The amphids are like a pore. They may be labial or post-labial coil or may have spiral apertures. They have annulated cuticles that may have projections and setae. Plasmids are located at their posterior end, if present. The excretory system of members of this class can be glandular or tubular.
They can be found in a wide range of habitats. Some species can be found in marine environments, others may be present in terrestrial environments. Their cuticle has undergone evolutionary modifications which allow them to adapt to a wider range of habitats. They reproduce at a much faster rate as compared to both classes Enoplea and Rhabditea. As a result, they are found in larger numbers.
The group Annelida includes earthworms, leeches, and polychaete worms. These types of worms are segmented. Term segmented means that their bodies are made from segments that are formed by subdivisions, partially transecting their body cavities. It is also termed as metamerism. Each segment contains a nervous system, circulatory system, and the excretory system. Segmentation increases the efficiency of movement as it allows muscle contraction to be localized.
The body wall of annelids is made up of circular and longitudinal muscle fibers that are surrounded by an acellular, moist cuticle. The cuticle is excreted by the epidermal epithelium. All members of this group, except leeches, have setae that are chitinous, hair-like projections from the cuticle. Sometimes, the seate are located on appendages that look like paddles. These are called parapodia.
These species are schizocoelous, having a large, well-developed true coelom (lined with mesoderm). Seate partially subdivides the celom in all members of this group except leeches. Hydrostatic pressure across all segments is maintained. This helps maintain the rigidity of the body, allowing the contraction of muscles to bend the body instead of collapsing it.
Annelids have well-developed internal organs. They have a segmentally-arranged, closed circulatory system. The digestive system in annelids is complete, along with anus and a mouth. The skin serves as the medium for gaseous exchange. Some species may have specialized gills or modified parapodia to carry out this function. Each segment has a separate pair of nephridia. The nervous system of annelids includes a pair of cephalic ganglia that are attached to double nerve cords. These nerve cords run along the length along the ventral body wall. each segment of the body has ganglia and branches. Annelids also have a combination of chemoreceptors, tactile organs, photoreceptors, and balance receptors. Some species may also have well-developed eyes and lenses.
Annelids are found in a variety of habitats, including terrestrial, marine, and freshwater environments. They can be active predators or passive filter feeders.
>a. Size and Symmetry
Annelids are bilaterally symmetrical. They can be as small as less than 1mm and as big as 3m in length. Smallest annelids that are known till date are as small as a few hundred microns.
All annelids have a true coelom. It is used as a storage area for the gametes and it serves as a hydrostatic skeleton for the movement. The segmentation of coelom has a major benefit for annelids. If there is damage to a worm’s body, the contents of coelom will be lost from the damaged segments only and the rest of the segments will remain unharmed, and the locomotion will not be affected.
c. Body Wall
The body wall or the cuticle of annelids is never molted or shed. The microvilli on the epidermis secrete a network of fibers which are composed of collagen and scleroprotein. As mentioned earlier, annelids have both, longitudinal and circular muscles. The circular muscle lies below the basal lamina and longitudinal muscle lies below the circular muscle.
Annelids are further divided into four classes which are:
The term polychaet means ‘many hairs’. Members of Polychaeta are found in terrestrial, marine, and freshwater habitat. They have an archetypical protosome development. Being annelids, they have a true coelom. They are bilaterally similar like all the members of the group Annelida.
They have a complete digestive system and a closed circulatory system. The nervous system is well-developed. The excretory system has metanephridia and protonephridia both. Each segment has a lateral epidermal setae. They can be hermaphrodite or dioecious. Fertilization takes place externally.
Example of the member of the class Polychaeta is sandworm.
Oligochaeta means ‘few hairs’. most of the members of class Oligochaeta are found in terrestrial environments. Only a few are found in freshwater habitats. The bodies of these annelids are metamerically segmented. The clitellum is present. They are hermaphrodites but cross-fertilization occurs in these annelids. The fertilization takes place externally. A formation of cocoon occurs.
Example of such annelids is an earthworm.
Leeches belong to the class Hirudinea. They are primarily found in freshwater environments but some may be found in terrestrial, marine, or parasitic habitats. The body of these annelids has a definite number of segments. Setae, tentacles, and parapodia are completely absent. They are hermaphrodites. Fertilization takes place internally. A larval stage is absent.
Archiannelids are strictly marine annelids. Their bodies are long. Parapodia and setae are usually absent. They may be hermaphrodite or unisexual. The development in these annelids is by indirect forming trochophore larva. Examples of archiannelids are Dinophilus and Protodrillus.
Thousands of worms are already known, with more types being discovered every now and then. It is believed that if all humans were eradicated from the face of this earth today, the earth would still survive because of the abundance of worms that are present, all known and unknown combined. There are many types of worms that are known and are subjects of various studies while there are also many types of worms that are still a mystery.
III. Common Parasite Worms That Cause Infection in Humans
The most common parasite worms to cause infections in humans are roundworms, tapeworms, pinworms, hookworms, and threadworms. Let’s look at each of them in detail.
A tapeworm, a type of flatworm, can infest humans by water. If you happen to drink contaminated water which has tapeworm eggs or its larvae, you are most likely to get a tapeworm infection. Another way in which tapeworms can make their way into human bodies is by eating raw or uncooked meat.
Tapeworms attach their heads to the walls of the intestine and they remain there. They produce eggs from the same place. These eggs mature into larvae and can migrate to other parts of the body. A tapeworm looks like a very long, white-colored ribbon. They can grow to be as big an s80 feet! It is hard to believe but it is true. Most shockingly, they can live in a human body for as long as 30 years!
Flukes are flatworms. Animals are more likely to get the infection. However, humans often get this infection too. The source of flukes is usually contaminated water, raw watercress, and some other freshwater plants.
Flukes reside in intestines, blood, and other tissues of the body. They do not grow too big. Flukes do not grow more than a few inches in length.
Hookworms are transmitted to humans through contaminated soil or feces. You can get hookworm infestation even if you walk barefoot on contaminated soil. They can easily pierce through the skin. They make a home in the small intestine. They attach their heads to the intestinal walls. they, unlike tapeworms, do not grow too long. They are usually less than half an inch long.
Threadworms or pinworms are not very harmful. Threadworm infestation is more common in children than in adults. They are a type of roundworm. Adult threadworms live in the rectum and colon. The female threadworm lays eggs at night around the anus. These eggs survive on clothing, bedding, and other materials. People get threadworm infection when the touch the eggs and then put hands in their mouths. If these eggs become airborne, they can be inhaled too, because of their small size. they can be passed in institutions or among children and caregivers.
These worms are harmless and can be treated easily.
5. Trichinosis worms
These worms are usually passed among animals. Humans may get them if they eat uncooked meat that may be a carrier of Trichinosis roundworm larvae. The larvae mature in the intestine and reproduce. They are also capable of traveling outside the intestines to other tissues and muscles.
IV. Worm Infestation
Worm infestation is extremely common in children. Since children are not under guard all the time, they may expose themselves to contaminated soil or may even drink contaminated water. Since soil and water are the most common habitats of worms, children are most likely to suffer from worm infestation.
The primary symptoms of a worm infestation are abdominal pain and diarrhea. Worms can live in the intestine. These intestinal parasites feed on the nutrition of the human and this may result in a visible weight loss of the affected person. There are many types of intestinal worms that are known to cause infections but as mentioned earlier, the most common ones are roundworms, tapeworms, pinworms, hookworms, and threadworms.
1. Common Causes of Intestinal Infections Caused by Worms
As mentioned above, children are more likely to catch worms. The most common causes of worm infections are listed below:
- Contact with infected surfaces such as contaminated soil that contains worm eggs and infected pets
- Consumption of infected water or food
- Improper hygiene
- Improper hand washing
Each worm causes an infection that shows a different set of symptoms. Common symptoms include weight loss, stomachache, irritability, bed wetting, and bloody stools. Some worm-specific symptoms are:
- Roundworm Infection
Dry cough, fever, diarrhea, and passing worms with stool
- Tapeworm Infection
Loss of appetite or eating too frequently, vomiting, nausea, jaundice, and sometimes malnutrition
- Pinworm Infection
Painful urination itching around the anus, and trouble sleeping due to itching
- Hookworm Infection
Coughing, wheezing, fatigue, and anemia
If any of the above-mentioned symptoms are observed, the doctor may recommend a stool test. As parasitic worms are usually eliminated through stool, presence of worms, their remains, eggs, or worm larvae in the stool sample may help diagnose a worm infestation.
Another test that is very commonly used for diagnosis of worm infection is a tape test. Female worms usually lay eggs outside the human body, around the anus, usually at night. This is the reason why itching around the anus is a common symptom. A tape test involves sticking of clear tape around the anus immediately after waking up or a few hours after falling asleep. Any eggs or worms around the anus will stick to the tape and it will help in the diagnosis.
If worms or not detected in the stool or in the tape test, a blood test may be conducted. Antibodies that are produced against parasites can help the doctor determine the type of worm that has caused the infection.
Colonoscopy may also be helpful if no evidence of worms was found in a stool sample or tape test.
Certain imaging tests like CT scan, MRI, and X-rays are also done to evaluate the extent of organ damage that may have occurred due to worm infestation.
The medication and course of treatment depend upon the type of worm that has caused the infection. Anti-parasite medicines or deworming medicines are available over-the-counter that are used for the treatment. Some important anti-parasite medicines are:
- Praziquantel: It is usually used for tapeworm infections. Adult worms get paralyzed by this medicine. They are detached from the intestinal wall, dissolved, and excreted through stool.
- Mebendazole: It is a common treatment for roundworm infection.
V. Earthworms-The Worm That Everybody Knows About
Whenever we say worm, earthworms are the first thing that pops in the mind because earthworms are extremely common and all of us have encountered them. Earthworms are delicate, harmless living things that reside in the soil. Since most of you are aware of what they are and what they look like, let us enlighten you with some facts of them that we are sure you did not know.
- Earthworms get paralyzed by too much light. Earthworms live under the soil and are accustomed to the darkness. They avoid light at all times. However, if they are exposed to bright light for about an hour, they get paralyzed.
- Earthworms can regenerate their bodies. They have 5 hearts near their head. If they are cut anywhere before their hearts, they can regenerate the lost segments.
- Worms have tiny hair on their bodies. They may look like smooth, slimy creatures but when you look closely, you will see the fine hair on their body. These hairs help them grip move through the soil.
- Earthworms breathe through their skin. They do not have lungs. Their skin is very thin which helps the exchange of gases to take place. The mucus on their skin serves as a medium through which oxygen is absorbed. They need moist conditions to survive. If an earthworm is kept in dry conditions, they will suffocate. Similarly, too much water can result in them drowning and dying.
- Earthworms are capable of digesting half of their body weight every day. They can process 10 pounds of organic matter throughout their life. They look tiny but their digestive system is super active and fast!
- Earthworms can feed on anything that was once alive. The only condition is, the material should be dead when they feed.
Worms are creatures that are found practically everywhere and it is important that you have knowledge about the types of worms that are present. With this article, we are sure you must have gained significant knowledge about worms and just how unique they are!