A parasitic round worm.
Any of a large group (phylum Nematoda) of unsegmented worms, tapered at both ends, including roundworms, pinworms, and hookworms; many species infest humans, producing disease.
A group of worm organisms that are common parasites of humans and animals. Unlike other worm parasites, including flukes and tapeworms, many species of nematodes are free-living, with life cycles that do not involve an intermediate host or vector, which is an insect or other organism that acts as a carrier. Infection is transmitted by these species from one host to another when the nematodes’ eggs, which contain infective larvae, are ingested. Hookworm, which is a nematode, is transmitted when the host’s skin is penetrated by infective larvae that have hatched from the nematode’s eggs. Several species of nematodes, including the filarial parasites that carry the infection filariasis, have life cycles that require a vector.
Any one of a large group of worms having an unsegmented cylindrical body, tapering at both ends. This distinguishes nematodes from other helminths. Nematodes occur either as free-living forms in the sea, fresh water, and soil or as parasites of plants, animals, and man. Hookworms and pinworms infest the alimentary canal. Filariae are found in the lymphatic tissues. The guinea worm and Onchocerca affect connective tissue. Some nematodes (e.g. Enterobius) are transmitted from host to host by the ingestion of eggs; others (e.g. Wuchereria) by the bite of a bloodsucking insect.
A class of the phylum Nemathelminthes that includes the true roundworms or threadworms, many species of which are parasitic. They are cylindrical or spindle-shaped worms that possess a resistant cuticle, have a complete alimentary canal, and lack a true coelom. The sexes usually are separate, and development usually is direct and simple.