Nematodes are worms with bilateral symmetry, with a very elongated body, cylindrical shape and a tapered tip. This is covered by the epidermis and, above it, by a cuticle. Under this first, there are longitudinal muscle fibers and, due to their arrangement, these animals move through undulatory movements.
They can be parasites, causing diseases in humans such as filariasis, ascariasis, hookworm, geography, trichocephalosis and oxyurosis. However, most of these individuals are free-living, they can be found in aquatic or terrestrial environments.
They are triblastic and, unlike flatworms, have pseudocoelom. This is located between the body cavity itself and the digestive tube. As they do not have a circulatory or respiratory system, the distribution and excretion of substances happen with the help of this primitive coelom, which also acts as a hydrostatic skeleton.
They have a complete digestive system and the nervous system consists of longitudinal nerve cords. The release of harmful substances takes place through a genital or buccal pore. They breathe by diffusion (skin breathing).
Most roundworms are dioecious, with sexual dimorphism: the female is larger, and has an anus; the male has a hook-shaped end and a vent. Fertilization is usually internal, but individuals may arise through parthenogenesis.
By Mariana Araguaia
Graduated in Biology
Source: Brazil School - https://brasilescola.uol.com.br/biologia/filo-nematoda.htm