Roundworms that may also be called nematodes , are a kind of worms which have a body round and long . They are worms that can vary in length from several millimeters to two meters. Roundworms are common to find in hot tropical countries . Children are more often affected than adults . Treatment is usually very effective, but eliminating pinworm infections is always a rather difficult process.

What are nematodes?

Nematodes are organisms that live in water , although they can also live on the surface . They are roundworms that have a digestive system that takes up most of their body.

  • Nematode characteristics
  • Classification of nematodes
  • Structure
  • Feeding
  • Reproduction
  • Breathing
  • Circulation
  • Nervous system
  • Nematode diseases
  • Nematodes in plants
  • Beneficial nematodes
  • Examples of species

Nematode characteristics

The most outstanding characteristics of nematodes are the following:
They are formed by a cavity filled with pseudocoelomic fluid that surrounds the individual’s organs.

  • They have a complete digestive tract with a mouth and anus.
  • Their body is elongated and cylindrical and they have good bilateral symmetry .
  • They can inhabit any ecosystem and are the most abundant animals on Earth.
  • They can be found in salt water , fresh water , on land, in tropical , polar regions and even in high mountains.
  • Most are parasitic , including a large number of human pathogenic species.
  • Its usual size varies between 0.1 mm to 2.5 mm in length and between 5 and 100 micrometers in thickness.
  • Their head can be differentiated from the rest of the body and they have sensory hairs .
  • Its surface is quite resistant and is called a cuticle.
  • The interior of the animal is composed of a liquid that serves as a hydrostatic skeleton and allows the distribution of nutrients .

Classification of nematodes

Nematodes can be classified as follows according to the different investigations carried out on them:

  • Secernénteos : this group of nematodes includes some species of round- type worms , generally inhabiting the earth . Males have only one testicle and the reproductive system is tubular in shape.
  • Chromadorea : they inhabit marine sediments more regularly. They have a more sophisticated pharynx than other nematodes. They have ring-like structures on their body and also have three esophageal glands .
  • Monhysterida : it has funnel-shaped pores that exchange gases and can have different types of teeth , which can in fact draw to the outside.
  • Dorylaimida : they inhabit humid soils , close to the roots of plants. Many of them feed on bacteria or other microorganisms . They can also parasitize plants and fungi.
  • Enoplea : Your esophagus is cylindrical or bottle-shaped. They are smooth , and some have fine lines on their bodies. Their excretory system is simpler than that of the other groups of nematodes.


These worms are cylindrical and long in shape , with bilateral symmetry . Its internal structure is relatively simple, and consists of an inner intestine and an outer muscular wall , which are separated by means of the pseudocele , which is a cavity that is filled with fluid. They have a length that varies from microscopic to 10 cm.

In the body wall of nematodes we can find a cuticle covered with collagen for protection, an epidermis that can be cellular or syncytial where the excretory ducts are located, a basement membrane and a lot of musculature below the epidermis that connect the nervous system with muscular arms; lastly, they have a reproductive organ pseudocoelom that functions as a type of skeleton.


Nematodes can feed on different types of materials. They can eat fungi , algae , some animals that are very small in size, are scavengers so they can eat fecal material and remains of other animals and insects.


The reproduction of these animals is carried out through parthenogenesis , however, most of the time they do it sexually . It is quite common to be able to distinguish the sex of nematodes, despite the fact that some species are hermaphrodites . During the sexual act, the male extends a spicule from his mouth and enters the female’s genital pore. When females become pregnant, they can produce hundreds of offspring through eggs .


Nematodes do not have any established respiratory organs and adults that have managed to position themselves and inhabit in the form of intestinal parasites are anaerobic , so they do not need oxygen, however, if oxygen is present, they use it.


Nematodes do not have any type of circulatory or vascular system . Nutrients travel through the pseudocoelom, which is driven by body movements and by their locomotion .

Nervous system

They have a ring of nerves located around the pharynx and different nerve branches arise from it . They also have sensory papillae , photoreceptor organs, and some have nerve and sensory glands.

Nematode diseases

Some of the diseases caused by nematodes are the following:

  • Ascariasis : it occurs due to contamination with human feces. Children are the most prone. The eggs of the nematode lodge in the small intestine invading the blood vessels of the mucosa and affecting the liver and lungs. It produces pneumonia, asthma and hives.
  • Hookworm : it occurs mainly in humid and warm lands due to fecal contamination . It affects the lungs and the gastrointestinal system.
  • Strongyloidiasis : they produce pruritic erythema and reach the lungs and small intestine where they develop into adult larvae. They cause diarrhea, encephalopathy, edema, hepatomegaly, and paralytic ileus.

Nematodes in plants

The most common are, for example: Meloidogyne sp., Pratylenchus sp., Ditylenchus sp., Heterodera sp., Tylenchus sp. (in fruit trees). They cause damage to the roots of plants and occur in greater quantities in sandy , hot and heavily irrigated soils . They are sensitive to droughts and cannot live without vegetation. So overall , the plants lose their color or take on a yellow hue, are malnourished and do not develop properly.

Beneficial nematodes

Some nematodes are not harmful to the whole, for example, earthworms help eliminate pests of insects that are on the ground where plants are grown as have a bacteria that can kill insects in just 48 hours. They do not affect humans and can kill weevils, fungi, mosquitoes, ground flies, some other types of worms, and fleas.

Examples of species

The nematode species are:

  • Adenophorea such as enoplide, isolaimide and troplonchida.
  • Chromadoria : araeolaimide, desmodoride, and monhysteride
  • Secernentea : like spirurida, ascaridida and camallanida.

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