The nematodes They are a group of animals that are characterized by having a cylindrical body, without segmentation. These living beings are very well distributed throughout the globe, although they are mainly in tropical environments..
They were first described in 1808 by the Swedish zoologist Karl Rudolphi and encompass approximately 20,000 species that can be found in both terrestrial and aquatic habitats..
Most nematodes have a parasitic lifestyle, requiring a host to develop. Many species of nematodes are causative agents of certain diseases, which mainly affect the digestive tract of the host, as well as its skin..
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Nematodes are eukaryotic organisms, whose DNA is enclosed within the cell nucleus, forming chromosomes. Their number is variable depending on the species.
They are triblastic organisms, because during their embryonic development they present the three known embryonic layers: ectoderm, mesoderm and endoderm. From these layers originate the different tissues and, consequently, the organs that make up the adult individual.
They have bilateral symmetry, which means that they are made up of two exactly equal halves, taking as a starting point an imaginary line in the longitudinal axis of the animal's body..
They are pseudocoelomed animals, since they have an internal cavity called pseudocele, which is not of mesodermal origin.
Most species are dioecious, although there are some others that are hermaphrodites. Asexual and sexual reproduction is observed in them, the latter being the most frequent and common.
They are also mostly oviparous (they reproduce through eggs) and almost all have an indirect development, since larvae emerge from the eggs that require some changes or molts to reach the adult stage..
The taxonomic classification of nematodes is as follows:
-Domain: Eukarya
-Animalia Kingdom
-Superphylum: Ecdysozoa
-Nematoid
-Phylum: Nematoda
-Classes: Adenophorea
-Secernentea.
Nematodes develop a vermiform body, which does not have cilia and no segments. They are whitish in color.
The body has a wall that is made up of several layers, these being (from the outermost to the innermost): cuticle, epidermis, muscles and pseudocele. Likewise, the body has a front end and a back end..
The mouth opening is located at the anterior end, which may be surrounded by lips or teeth. The rear end is different in females and males. In the latter, it generally ends in a curvature and also has structures known as spicules, which are used during copulation..
The digestive system of nematodes is complete, with an entrance hole (mouth opening) and an exit hole (anus).
The oral cavity is surrounded by some structures such as lips and teeth, among others. This will depend on the type of diet according to the species. Immediately afterwards comes the pharynx, which is normally closed. It only opens for the passage of food.
After the pharynx is the intestine, which is where nutrients are absorbed and which finally ends in the anus.
It is made up of longitudinal nerve fibers that emerge from a ring that surrounds the pharynx. So it has a fairly simple structure.
The excretory system is not the same for all nematodes. Some may be tubular and others glandular..
In the tubular excretory system, there are two tubules, which are connected by a kind of commissure.
On the other hand, the glandular excretory system is characterized by presenting two kidney cells that are large and lead to an excretory pore..
The female reproductive system, depending on the species, may have one or two ovaries, which connect with an oviduct, which ends in a seminal receptacle and finally in the gonopore..
In the case of the male reproductive system, there is a testicle, a vas deferens, the seminal vesicle, and the ejaculatory duct. In addition to this, they present copulatory spicules.
The phylum Nematoda is classified into two large classes: Adenophorea and Secernentea. Between them they cover a total of 5 subclasses, 2 in Adenophorea and 3 in Secernentea.
They are a group of nematodes that present certain characteristics such as: setosus sensory organs, five esophageal glands or perhaps more.
They also have posterior sensory organs known as postlabial amphidia, which in turn are made up of sacs. They have sensory papillae distributed throughout the body. Their bodies are covered by a kind of very resistant cuticle that is made up of four layers.
In addition, when they have an excretory system, it does not have lateral channels, but only ventral cells, which can be in number of one or more. Sometimes it is totally absent.
They can be found in any type of habitat, whether terrestrial, marine or freshwater. A large percentage of its species is free-living, although there are also important parasites.
This class encompasses two subclasses: Enopila and Chromadoria.
The members of this subclass of nematodes are characterized by their smooth bodies, without any type of lines or rings. In addition to this, their anterior sensory organs, known as amphidia, are highly developed and can be shaped like ovals, stirrups, or pouches..
Most of these are free-living, however, to this subclass belong some orders within which there are parasitic nematodes that must be within their host to survive..
This subclass encompasses six orders: Mermithida, Dorylaimida, Enoplida, Muspiceida, Trichiurida, and Trichocephalida. Of these, the best known and studied are Enoplida and Dorylaimida.
The nematodes of this subclass have three esophageal glands, in addition to presenting a much more developed and complex pharynx than that of other nematodes..
Their bodies are not completely smooth, but the presence of rings on their surface is evident. This is a distinctive element with respect to the other subclass, Enopila. Sometimes your cuticle may have some kind of projections or mushrooms.
They also have an excretory system that can be of two types: glandular or tubular. The specimens that are female have one to two ovaries. They have highly elaborate anterior sensory organs (amphidia) that are generally spiral-shaped.
This subclass in turn comprises seven orders: Plectida, Menhysterida, Desmodorida, Chromadorida, Araeolaimida, Rhabditida and Desmocolecida..
Its name is a word derived from Latin whose meaning is an excretory organ. The excretory apparatus is tubular in type. Its body is covered by a cuticle on the surface of which you can see radial striae of the basal type..
In addition, its cuticle has several layers (usually 4). The amphidia, which are its main sensory organs, are located on the lateral part.
The nematodes that belong to this class are an excellent example of sexual dimorphism, in which there are marked morphological differences between females and males..
Females are often much larger than males and males have certain structures that they use for copulation, such as spicules at the terminal end of their tail. Likewise, the tail of females usually ends in a point, while that of males does so in a characteristic curve..
This class is classified into three subclasses: Spiruria, Diplogasteria, and Rhabditia. However, there are specialists who do not consider this as such, but go directly to the orders that are within the Secernentea class. Accordingly, the orders that are part of this class are: Strongylida, Rhabditida, Ascaridida, Spirurida, Diplogasterida, Tylenchida, Drilonematida and Camallanida.
Taking this into account, the most representative orders will be described below..
Some of the best known parasites belong to this order, such as Ascaris lumbricoides Y Enterobius vermicularis. Among its representative characteristics we can mention the presence of three lips around the oral opening and fins on both sides of the body. They are cream-colored and robust in appearance.
In general, these parasites tend to lodge in the small intestine of mammals such as cats, dogs and even humans..
Organisms of this order are characterized by having only two lips around the mouth. Its esophagus is divided into two parts: a posterior one, which is long and glandular in nature, and an anterior, short and muscular..
They are parasitic in life, and most of the time they require, to correctly complete their life cycle, the intervention of some arthropod, such as the fly of the genus Chrysops that participates in the parasite cycle Loa loa.
Its anterior sensory organs (amphidia) have a lateral location. This order encompasses a total of 10 superfamilies, of which the best known is Filarioidea.
Free-living worms belong to this order, as well as zooparasites (parasites of animals) and phytoparasites (parasites of plants). Some of the parasites inhabit the intestine of mammals and are capable of causing diseases such as strongyloidiasis.
They have a thin cuticle, which has some rings, as well as stretch marks in the longitudinal direction ... They are whitish in color. They can have up to six lips around the mouth. Covers about 9 superfamilies.
Nematodes of this order are of great importance in veterinary medicine, since many of them are causal agents of pathologies in mammals such as pigs, horses and ruminant animals..
The mouth capsule of these animals is variable in shape and size. Males have a structure known as a copulatory bursa. In addition to this, here you can find organisms whose life cycles are direct and others with indirect life cycles that require an intermediate host to be able to develop..
This order is made up of 7 superfamilies, which group a total of 27 families.
In nematodes, the two types of reproduction can be observed: asexual and sexual, the second being the most common. However, there are species in which asexual is more frequent..
Asexual reproduction is one that does not involve the fusion of any type of sexual cells, so the interaction between two individuals is not necessary..
There are many asexual reproduction mechanisms. However, in nematodes the one that is most observed is parthenogenesis. This is a mechanism that consists of the female reproductive cells (ovules) beginning to undergo a series of mitotic divisions until they become an adult individual. It is believed to be induced by certain environmental conditions.
Sexual reproduction is the one most commonly observed in nematodes. The foundation of this type of reproduction is the fusion or union of male and female gametes (sex cells) in order to generate a new individual..
In nematodes this type of reproduction contemplates internal type fertilization. This is that fertilization occurs inside the body of the female.
Most of the male specimens have structures known as spicules, which are sometimes associated with copulatory bags. These spicules are used as a copulatory organ, through which the male introduces his male gametes inside the female's body to give rise to fertilization..
Likewise, nematodes are oviparous organisms, which means that they reproduce by eggs. Once fertilization occurs, the females are capable of producing thousands of eggs. Some species can even produce millions of eggs.
Larvae emerge from the eggs which, in order to become an adult nematode, need to go through various transformation or molting processes. Thanks to this, it is possible to affirm that nematodes are animals that present an indirect development.
Nematodes are heterotrophic organisms, as they do not have the ability to synthesize their own nutrients. Taking into account that they are parasites, they feed at the expense of their hosts, according to various mechanisms.
There are some nematodes that attach to the intestine of the host and feed on the blood that they absorb there, therefore they are hematophagous.
Likewise, there are others that, despite the fact that they are housed in the host's intestine, do not attach to the wall of the intestine to absorb blood, but instead feed through an absorption process throughout their body. These feed on the nutrients ingested by their host.
Likewise, there are nematodes that are parasites of plants and are fixed mainly in their roots, feeding on the nutrients of the plant and its internal tissues, which they gradually destroy..
Many nematodes are parasites of animals, mainly mammals such as dogs, cats, coyotes, rodents and even humans. Most are fixed in the intestine and feed on the blood of its host, causing, among other things, anemia, as well as intestinal disorders.
This parasite belongs to the order Trichurida. It is also known as a whipworm, due to its shape. It is cylindrical, with a very wide part and a very thin part. They are endoparasites that are mainly found in the intestines of some primates, such as humans.
It is responsible for trichuriasis. This is a disease in which the digestive tract is markedly affected, with symptoms such as loss of appetite, diarrhea with bloody stools, and severe abdominal pain. If the parasites are many, there may be a rectal prolapse or an obstruction.
It is a parasite belonging to the order Strongylida. Like all parasites, it requires living inside a host. In this case, its most frequent hosts are humans and other mammals such as dogs or pigs..
They are typical of tropical environments, in which the humidity and temperature conditions are ideal to allow their eggs to develop and their larvae to form. They are quite small, since they barely measure up to 1.5 cm.
The disease it causes is necatoriasis, also known as hookworm. The symptoms they present are quite varied, depending on the organ it affects. They can develop symptoms at the level of the skin, lungs and blood, among others.
It is one of the best known and studied intestinal parasites. It belongs to the Secernentea class. It is among the largest nematodes, since the female can measure up to 30 cm and the male about 20 cm.
Ascaris lumbricoides it is the causative agent of a disease known as ascariasis. This presents symptoms at the level of the intestine, such as diarrhea, vomiting and bloody stools; there are also pulmonary or respiratory symptoms such as chronic cough, difficulty breathing properly and high fever.
This is a parasitic disease that must be treated as quickly as possible, since if not, the parasites continue to develop and grow in the intestine, potentially causing intestinal obstruction, with consequences that can even be fatal..
This parasite is quite frequent in the population, especially among children. They belong to the Oxyuridae family, which is why they are also known as pinworms.
Its life cycle takes place entirely in the human body. The main symptom of infection with this nematode is intense anal itching (or itching). This is caused by the presence of the eggs in the folds of the anus.
Infection by this parasite is a bit difficult to eradicate, since reinfection is constant, since the person tends to scratch the anal orifice, acquiring microscopic eggs under the nails and when they put their hands in their mouth, they ingest them again.
Ancylostoma duodenale it is a nematode whose main host is the human being. It is the main responsible for a disease known as hookworm.
This disease is quite common, especially in areas of the world where it is difficult to take extreme hygiene measures. In humans, it causes damage to most of the body's organs, such as the skin, lungs, digestive tract, and heart..
These damages are caused by the transit of the larvae through these organs and by the fixation of the adult parasites to the intestinal wall, absorbing the blood of their host..
These are two very similar nematodes that host mammals such as cats and dogs. In these they cause intestinal symptoms such as diarrhea, constipation and even, if the parasitosis is very intense, it can generate an obstruction at the level of the intestine.
Although they are parasites of these animals, they can occasionally infect man, in which they can cause long-standing infections that eventually greatly deteriorate organs such as the eyes, liver, lungs and brain, among others..
Some of the nematodes known today are veritable pests of agricultural crops. This is because they have as hosts certain plants, to whose roots they attach themselves, feeding on them and damaging them in a large proportion.
These are nematodes that greatly affect a diverse number of plants, causing damage that eventually leads to their death..
Among the consequences of an infection by these nematodes in plants are: chlorosis, growth stunting and wilting, in addition to presenting certain protrusions at the level of the roots, called knots.
These species of cysts or bulbs interfere with the normal functions of the root, preventing it from absorbing water and nutrients from the soil and therefore dying..
Also known by the name of "Soy cyst nematode", it is a widely known parasite that affects the roots of this plant, compromising its development..
The effects that this parasite causes on plants are varied. These include destruction of the conducting vessels at the root level, which eventually generates tissue necrosis, inhibition of root growth and decreased seed yield..
Its name is due to the fact that when the female dies it forms a kind of hardened cyst in the roots of the plant, protecting the eggs it houses inside. When the eggs hatch, the larvae penetrate the root and continue their cycle.
This is a genus of parasites that is also known as dagger nematode, since they have an elongated and thin structure at its head end similar to that instrument. Through this structure, the parasite attaches itself to the root of the plant.
The damage they cause to the plant is that they function as vectors of some viruses, mainly nepovirus, which causes serious damage to plant tissues, representing one of the worst pests for crops..
This is a genus of parasites that affect plants that belong to the Solanaceae family. It forms small cysts on the roots of these plants, greatly interfering with the regular processes of the plant..
Paratylenchuss hamatus it is a phytoparasite that can infect a wide variety of plants. Among the obvious symptoms that a plant is infected by this parasite can be mentioned: chlorosis, atrophy of plant and root growth, leaf fall, among others.
This parasite works as a vector for trobaviruses, which cause terrible damage to the roots of plants, specifically at the tips of these.
As a consequence of the action of the parasite and the virus on the root, it stops growing and elongating, the root adopting a "stubby" shape. Eventually, the root stops fulfilling its function, which has to do with the absorption of nutrients and water, so the plant begins to degenerate, until it dies.
This is a parasite that affects a large number of plants, specifically at the root level. Through its mouth, the guano attaches itself to the root of the plant, penetrates its tissues and feeds on the various tissues of the plant..
Among the damages caused by this parasite in the plant are mentioned chlorosis, fruit spots, deficit in the growth of the plant and necrosis in the tissues, especially in the roots of the plant.
Because these effects are similar to those of many other nematodes, an exact diagnosis is difficult. However, it constitutes a terrible pest for agricultural crops.
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