Nematodes are roundworms that have bilateral symmetry and lack a complex body plan.
Roundworms have a simple nervous system, no digestive system or respiratory system, and possess only longitudinal muscles.
They move by contracting these muscles, causing the worms to whip back and forth because
they have nothing to brace these muscles against.
Nematodes excrete wastes using specialized cells or canals, but do not contain flame cells, as the flatworms do.
There are around 12,000 species of Nematodes that have been identified,
although studies suggest that there could be up to about 500,000 species.
Nematodes include both free-living and parasitic species, many of which can be harmful to humans.
Nematoda includes common roundworms, which infect many humans worldwide, hookworms,
trichina worms, which are responsible for trichinosis, pinworms, and filarial worms,
which cause the devastating diseases elephantiasis and river blindness.
The damage nematodes can cause in humans should not be underestimated, nor should their abundance in the world.