Phylum Nemathelminthes: [Nema-Thread, Helminthes-Worms]

• This phylum is also known as nematode or aschelminthes. The organisms are commonly known as roundworms or threadworms.
• Habit and Habitat: Most of them are pathogenic parasites i.e., they live in other animal’s [host] body and causes disease in them. Some are free living in soil and water.
• Symmetry: they are bilaterally symmetric [left and right side of the body has same design].
• Body cavity: They are pseudocoelomate, i.e., true cavity is absent.
• Body differentiation: They are multicellular with developed tissues. Real organs are absent.
• Germ layer: They are the first triploploblastic animals.
• Body organization: Body is worm-like, elongated, narrow and cylindrical or slender, i.e., tapering at the two ends. They are usually transparent.
• Skeleton:  true skeleton absent but body is covered with tough, resistant cuticle.
• Life processes:

1. Alimentary canal/ digestive tract present having two openings- mouth and anus. First group in which straight and complete alimentary canal is present.
2. Blood circulatory system and respiratory system is absent.
3. Excretion takes place through excretory pore and anus. They also have special excretory organs, glands and excretory canals.
4. Nervous system is simple, comprised of simple brain and two nerve cord.
5. They are unisexual; both male and female sex organs are located on separate body.
6. Reproduction is usually sexual.

Examples:

Round worm [Ascaris], pin worm [Enterobius], Filarial worm [Wucheria] etc.

Note:

Ascaris causes ascariasis, wucheria causes elephantiasis, enterobius causes enterobiasis.