|Round worms or Nematodes belong to the phylum of invertebrates. The body form is usually porrect and spindle-shaped. The length varies from microscopic to several meters. The digestive tract is straight with a mouth cavity at the front and an anus at the back. Between the body wall an intestine is located in the primary body cavity (pseudocoelom) filled with liquid and differs from the secondary (coelom) by the absence of an epithelial lining. Outwardly, the body is layered with a firm cuticle, at the bottom is a thin layer of live hypodermis and beneath that are cords of lateral muscles. Peculiar to nematodes are four hypodermic cushions (“chordes”) pressed into the body cavity: dorsal (spinal), ventral (abdominal) and two collaterals. Within the first two cushions are nerve trunks, when it concerns collaterals sensory nerves and excretory canals. The animals are usually dioecious but hermaphrodites are known too. The larvae are hatched out of inseminated eggs either in the outside environment, or in the genital tracts of the female itself. Reminiscing arthropods, when larvae grow and mature, shed periodically the cramped cuticle and acquire a new one.
After insects, this is the second type in the animal kingdom by diversity-wise. It is considered that nematodes are counted several hundred thousand types. They can be seen in any climates suitable for life and play a significant role in ecosystems. Billions of free-living nematodes can inhabit a territory of 1 hectare and they, it seems, enrich the soils fertility. Some types are plant parasites; they infest roots, stems and seeds of many valuable crop cultures. Among nematodes also known are parasites and commensals of animals of all large systematic groups including animalcular. The bio-systematics of round worms is not well developed. It is divided into two sub groups: phasmids (Phasmidia) and amphids (asphimidia). The difference between them is explained by the presence or absence of a tail chemoreceptors (phasmids) and also by peculiarities in structure - the so called side organs (amphids) which are supposed to be with chemoreceptor functions and are located symmetrically on the external side parts of the head area.
Phasmides are related to the majority of soil as well as parasitic nematodes. Among the phasmid group of nematodes the following are interesting: The genus Rhabditis is combined of free living types. The dwarf thread worm (Strongyloides stercoralis) causes strongyloidosis -nodular worm disease with an affect like “butterflies in the stomach” and skin eruptions. The vinegar eel (Turbatrix aceti) is often seen in unsterilized vinegar. Necator americanus (in the tropics) and Ancylostoma duodenale (in Old world) causes dochmiasis – helminthiasis fraught with anemia due to loss of blood in the intestinal tract damaged by parasites. Infant pinworm (Enterobius vermicularis) is a widespread tapeworm causing itchiness in the anal area and perineum. Ascaris lumbricoides is the cause of ascariasis affecting the lungs at the first stage and the intestinal tract at later. Very important from a medicinal point of view is the group of filarial and filarial alga which affects the hypoderm and lymphatic system filariasis and filariatosis. One among the types of this group is the Wuchereria bancrofti which settles in the lymphatic tubes, resulting in their inflammation and, in most severe cases, by blocking them develop elephantiasis. Filaria (Onchocerca volvulus) affects the skin and eyes (onchocerciasis) and may cause the so called river blindness (carriers are the midges, plentiful along the tropical rivers). Philaria Loa Loa causes loaiasis or Calabar swelling, featured with temporary hydrops and conjunctivitis.
Generally water nematodes and only several parasitic types are related to the non-phasmid sub group. Trichinella spiralis causes trichinellosis with the eyelids swelling and severe pains in the muscles (here larvae stay), but the giant kidney worm (Dioctophyma renale) mainly affects the kidneys (dioctofimosis).