Final answer:
Parasites are classified as ectoparasites or endoparasites, with ectoparasites living on the host's surface and endoparasites living inside. Parasitic helminths mainly include roundworms (Nematoda) and flatworms (Platyhelminthes), with significant human pathogens like hookworms, tapeworms, and flukes.
Step-by-step explanation:
Parasites are organisms that live on or inside a host organism and benefit at the host's expense. They can be classified as ectoparasites or endoparasites. Ectoparasites live on the surface of their host, whereas endoparasites live inside the body of their host.
Parasitic Helminths are divided into two main groups: Nematoda (roundworms) and Platyhelminthes (flatworms). These groups include significant pathogens to humans. Nematoda possesses a round body structure and includes species such as roundworms, pinworms, hookworms, and whipworms.
Platyhelminthes, on the other hand, can be segmented or non-segmented; the segmented ones are known as cestodes (tapeworms), such as beef, pork, and fish tapeworms, and the non-segmented ones are called trematodes (flukes).
Endoparasitic helminths, such as certain trematodes and cestodes, occupy the digestive systems of their vertebrate hosts. Some helminth parasites are notable for their complex life cycles, involving multiple stages and different hosts. Within the flatworms, other than parasitic trematodes and cestodes, there are also ectoparasitic groups such as monogeneans.