Nematodes. How are they built, what are they characterized by?

We associate nematodes with parasites, harmful organisms that destroy crops and cause disease. In a way, this is true as they can ruin some types of crops as well as human health. Some varieties of nematodes, however, are useful and are used in biological or integrated plant protection. What are Nematodes? How do they reproduce?

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1. What are nematodes?

Roundworms (roundworms) are a type of invertebrate animals, formerly classified as a group in the roundworm type. They live in water and soil.

Some species are found in waters up to 3.6 km below the earth's surface - deeper than any other known multicellular organism. Usually these are plant and animal parasites. Nematodes are among the most common diseases in humans.

2. How are nematodes built?

The body shape of the nematodes is strongly elongated and characterized by dimorphism (of various dimensions). Usually they are small organisms, their length ranges from 0.3 mm to 10 cm, but there are nematodes about 1.2 m long, and one of the species reaches up to 8 m.

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2.1. External structure of the nematode

The outer shell of the nematode body is an integumentary sack, which consists of the epithelium, a single layer of muscles and the cuticle.

The cuticle of the nematodes, called the cuticle, is an acellular protective layer that only permeates water and gases. It is made of a protein substance, thanks to which these organisms are very resistant to adverse environmental conditions and poisons.

The epithelium (hyporderm) is located under the cuticle and its structure depends on the size of the nematode. The epithelium forms thickenings called hypodermal rollers that run along the length of the body.

The muscle layer is made up of four pairs of longitudinal muscles. The body cavity is filled with serous fluid, which gives the body elasticity. These muscles also replace the circulatory system, distributing nutrients.


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2.2. Internal structure of the nematode

As for the internal structure of the nematodes, it looks like this:

  • have a hydrostatic skeleton;
  • the digestive system is in the form of a tract and is divided into three sections: anterior, middle and posterior; it begins with a mouth leading to a throat that connects with the intestine and ends with an anal opening which, however, may be reduced in some species;
  • they carry out gas exchange with the surface of the whole body, they do not have a respiratory system; can breathe anaerobically;
  • nutrients circulate through the nematode through the serous fluid - it has no circulatory system;
  • the nervous system consists of the pericardial ring (peropharyngeal ring) with 5 ganglia and nerve trunks connected by transverse commissures;
  • the excretory system is composed of 2 ducts having a common outlet - they lead through the whole body in the lateral hypodermal dikes, and the outlet is the excretory opening; its main task is to regulate the osmotic pressure of the organism; the nematode also has phagocytic cells which retain and store metabolic products insoluble in water; The waste nematodes thus collected are kept for the rest of their lives.

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3. How do nematodes reproduce?

Nematodes reproduce only sexually. Most of them are dioecious, and some show marked sexual dimorphism.

Females are usually larger, with males folded back. Most individuals of this species are oviparous. The larvae are very similar to the adult representatives of this species, although they are smaller and have no reproductive organs. When they grow - they moult - they shed the old cuticle and a new one appears in its place.

4. Representatives of nematodes

Among the representatives of this species, we can mention, among others:

  • parasites of animals and humans: human pinworm, trichinella, roundworm, duodenal hookworm, whipworm;
  • microbionts;
  • micetophages;
  • acetic nematode;
  • potato nematode;
  • beetroot nematode;
  • harmful root rot.
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