Roundworms are parasitic invertebrates that can inhabit the human body, primarily living in the intestines. The six most common types of roundworms include pinworms, ascaris, hookworms, whipworms, strongyloides and trichinella spiralis.Roundworms vary in size, transmission and habitat.Though most roundworm infections are not life threatening in healthy people, many cause uncomfortable and sometimes serious symptoms.he six most common types of roundworms include pinworms, ascaris, hookworms, whipworms, strongyloides and trichinella spiralis. Roundworms vary in size, transmission and habitat.