- Elongated cylindrical round body
- Body cavity is a pseudocoelom (false body cavity)
- Alimentary canal opens at the two ends, mouth and anus.
- Sexes separate, males smaller than females
- Mostly parasitic in animals but some live freely in the soil.
- Ascarisis a common roundworm, parasitic in the intestine of humans.
- Pinworm and Wucheria (Filariaworm) are some other examples.