The nematodes ( Nematoda ) belong to the junction of the Némathelminthe S or towards rounds . They have a bilateral symmetry, the body is not segmented. The nematodes are covered with thick a Cuticule. They carry out a free or parasitic life. This group contains worms whose cycle does not require an intermediate host (Monoxène). It is convenient to classify them according to the mode of transmission.
Physiology
The Nematodes are pseudo-cœlomates triploblastic métazoaires. The nematodes have a digestive Tract complete (i.e. stops and anus). On the other hand, they have neither breathing apparatus neither circulatory apparatus nor of muscular tunic.
The pseudoone corresponds to the Blastocèle which is a cavity which is formed during the embryonic development. To the Annélides the blastocœle goes perdurer on the level of the digestive Tract and the Nervous system. Breathing is done by diffusion through pores which bore the impermeable cuticule. This diffusion is passive i.e. the organization does not have any more of the blastocœle, the blastula form a cavity between the digestive tract and the derm. This cavity is called secondary cavity. The nervous system is made of a cephalic ring which are prolonged by a ventral nervous cord and a dorsal nervous cord.
Protection
The surface of the body is striated with line red and black but is not to in no case a Métamérie. The animal has a hydrosquelette under pressure which rests on its Cuticule what gives them this circular form. The cuticule is secreted by the skin. The animal is covered with three layers, two pseudo Kératine and the third of Collagène, which forms a inextensible Exosquelette. The nematodes thus have a discontinuous growth (one speaks about Ecdysozoaires) by increase in the cellular matrix because the nematodes have the characteristic to have always the same number of cells for a given species. They are dioïques and have 4 youthful stages. Studies Génétique S showed that the Arthropode S were very close to the nematodes. At the nematodes parasitizing the digestive system of other species, the cells myoépithéliales are surrounded by myofilament what prevents digestion and gets a physical protection.
Locomotion
The nematodes have mycrofilaments directed in the antéro-posterior direction, the nematodes can contract only in the antéro-posterior direction, which gives them a vague displacement, by undulation. These movements are not very effective in water, but they are facilitated by the presence of particles on which the nematode can be pressed.
Ecology
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the free nematodes meet in very diversified environments: brackish fresh water, water, salt water. Anguillula aceti lives in the vinegar. Caenorhabditis elegans lives in the ground, it is a model organization in biology.
- the parasitic nematodes attack with the Invertébré S and the Vertébré S, alive in the cavities (intestine, kidney), in the blood-vessels or fabrics. The Oxyure S are found in the digestive tract of the Arthropode S and Vertebrate ( Enterobius vermicularis parasite the human one). Ascarides live the large intestine of the Mammifère S ( Ascaris lumbricoides is lodged in the intestine of the Man). The telegraphic one of Bancroft ( Wuchereria bancrofti ) parasite the lymphatic vessels of the Man and can cause the elephantiasis. Trichine ( Trichinella spiralis ) causes trichinose.
- There exists a great number of parasitic nematodes of the plants: Tylenchus tritici is the anguillule corn, the nematodes with cysts ( Heterodera …), nematodes in Wales ( Meloidogynous …).
Classification
S and S- class of the Adenophorea
- subclass of the Chromadoria
- subclass of the Enoplia
- class of the Secernentea
Between 15 000 and 25 000 species are known and described, but there would exist about it much plus : of 250 000 with 500 000 following sources.
Parasitic nematodes
A certain number of nematodes parasitize the human one and are responsible for Parasitose S:
- Ascariasis by Ascaris ( Ascaris lumbricoides ).
- Anisakiase by different Anisakidae.
- Trichocéphalose by Trichocéphale ( Trichuris will trichiura )
- Oxyurose by Oxyure ( Enterobius vermicularis )
- Ankylostomose by Ancylostoma duodenale and Necator americanus
- Anguillulose by Strongyloides stercoralis
- Trichinose or trichinellose by Trichinella spiralis
- Filariose S
- Trichostrongyloïdose S
- Angiostrongyloïdose S
- Capillariose S
- Larva migrans by Toxocara cani and Toxocara gloss
Parasites of insects:
- Heterorhabditis bacteriophora: nematode entomopathogene parasitizes Otiorrhynque, and larva of the cockchafer called also the white Ver.
See too
Related articles
Taxonomic references
External bonds
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