The animal belonging to the Phylum Nemethelminthes are commonly called round worms or thread worms or bag worms or nematode.
The phylum Nemethelminthes includes about 15,000 species. Out of which about 15 species are parasites of man.They are spread through insanitary conditions, or by vectors. Many nematodes infect plant roots, whereas others infect animals. Free living microscopic nematodes like Rhabditis live in soil rich in organic matter.
1. Nematodes are either free living or parasitic.
2. They possess an organ system organization.
3. They have a tube within a tube body plan.
4. They are bilaterally symmetrical.
5. They are triploblastic animals.
6. They are pseudo coelomate animals.
7. The body is tubular tapering at both ends and is covered with a thin cuticle.
8. Epidermis is multinucleated.
9. They have a tubular alimentary canal within their body consisting of mouth, pharynx, intestine and
anus.The mouth may possess teeth to cut and pierce the tissues. The muscular pharynx helps in sucking
food from the host.
10. Circulatory and respiratory system are absent.
12. Excretory system includes two longitudinal canals in the lateral cords and shorter anterior excretory canal
which opens to the exterior through the excretory pore.
11. Theyshow flexible body movements.
12. Nervous system is present.
13. Sexes are separate. They exhibit sexual dimorphism. The male is smaller than the female. Males have
copulatory spicules which help inthe process of copulation.
14. Fertilization is internal. The zygote has a thick wall to survive adverse conditions.