Roundworms are smooth, thin, tube-shaped worms that are at both ends. Roundworms are the common worms on the earth. Some roundworms reproduce inside their host’s .

open, most common, intestines

Explanation:

They have an open digestive system with a mouth opening that connects straight to their anus. They are the most common animal on the planet and include earthworms. A lot are parasitic and reproduce and live in a hosts intestines. their eggs and sometimes the worm themselves can be passed through feces. Then another animal may eat it or someone steps in it and they become infected