Pinworms (Enterobius vermicularis) is a parasitic roundworm in the phylum Nematoda, and the class of Secernentea. They only attach to humans on their stomachs as eggs. The eggs hatch in the duodenum and develop as larvae in the small intestine. They live as adults in the colon and breed there. Being infected by a pinworm isn't fatal, seeing as they die within a few weeks of entering the colon. Like the hookworm, they have cilia and layers of muscle activated by two nerves that allow them to move around. They have longitudianl body symmetry. The muscles and nerves are almost connected because they are very close to each other and run down the length of the body.