Roundworms belong to the kingdom Animalia and the phylum Nematoda. Roundworms are unsegmented, smooth and strand-like worms that can grow to a length of 4 feet. There are approximately 15,000 species of roundworms, and many are parasitic organisms.
Some different types of worms include hookworms, pinworms and trichinella. These are parasitic creatures that can infest humans and cause infections.
Some characteristics of a roundworm are that it lacks body structures, such as a heart, respiratory tract or blood vessels, but it does have a digestive tract that includes intestines and an excretory organ. Some types of roundworms can reproduce rapidly and lay over 200,000 eggs per day. Roundworms can be found in different environments, such as water sources and soil.