Parasitic Worms

PARASITIC WORMS (Helminthes), helminths, worms, an artificial group of animals belonging to various phyla into which the former phylum Vermes L., 1758 has disintegrated, united by a parasitic mode of life. From the phylum of flatworms (Platodes), all representatives of the classes Trematoda and Cestoda are without exception helminths. The class Turbellaria is represented in the vast majority by free-living forms; parasitic worms among turbellarians turn out to be a few species of the order Temnocephala, living on the body. From the phylum Acanthocephala, all representatives without a single exception are parasitic worms. From the phylum Nemathelminthes, the main representatives of parasitic worms belong to the class of nematodes (Nematoda), among which there are parasites of both humans and animals, as well as a wide variety of plants. Representatives of the class of hairworms (Gordiacea) lead a parasitic mode of life only in the larval stage and in the nymph stage, with the hosts of gordiids being various, mostly aquatic insects. From the phylum of rotifers (Rotatoria), the majority of representatives lead a free-living mode of life; parasitic worms among rotifers turn out to be isolated species parasitizing either lower animals (echinoderms, crustaceans) or on certain plants. From the phylum Annelida, parasitic worms are represented by the class of leeches (Hirudinea), with some forms being stationary parasites, others temporary parasites, and finally thirdly leading a predatory mode of life and therefore cannot be considered parasitic worms. Isolated species of bristle-footed annelids (Chaetopoda) must be classified as parasitic worms, such as Branchiobdelia, localized on the gills of the crayfish. From the given review of parasitic worms, it is clear that they are completely heterogeneous organisms not connected with each other either by community of origin, nor by similarity of anatomical structure, nor by the unity of the biological cycle. The only feature uniting them is a parasitic mode of life. Thus, parasitic worms have to be defined as follows: these are such representatives of the phyla Platodes, Nemathelminthes, Acanthocephala, Rotatoria, and Annelida that lead a parasitic mode of life in animals (including humans) and plants. The science that studies parasitic worms and the diseases of humans, animals, and plants caused by them is called Helminthology.