The phylum Aschelminthes is also known as Nematoda, and its members are nematodes. The members of this phylum are roundworms, and many are microscopic.
Roundworms have many of the same characteristics of flatworms: for example, bilateral symmetry and cephalization. They also have a digestive tract open at both the mouth and anus. This tract is suspended in a body cavity that is said to be false, so it is called a pseudocoel.
Many species of roundworms are free‐living organisms that help consume dead plant and animal matter. Several parasitic roundworms cause human diseases, including trichinosis, hookworm disease, and elephantiasis.