By Dr Ananya Mandal, MD. Helminths are parasitic worms that feed on a living host to gain nourishment and protection, while causing poor nutrient absorption, weakness and disease in the host.These worms and larvae live in the small bowel and are referred to as intestinal parasites.ome of the features of the different groups of the helminths include: 1  The trematodes or flatworms are flat, leaf-shaped and unsegmented. 2  Nematodes are cylindrical and have lips, teeth and dentary plates. 3  The cestodes or tapeworm is segmented and hermaphroditic.