HEALTH & DISEASE ZOOLOGY A  B  C  D  E  F  G  H  I  J  K  L  M  N  O  P  Q  R  S  T  U  V  W  X  Y  Z                    HOME ABOUT CATEGORIES SITE MAP COPYRIGHT ADVERTISE CONTACT entire Web this site nematode (roundworm) A free-living soil nematode Any of a large group of worms having an unsegmented cylindrical body, tapering at both ends. This distinguishes nematodes (known commonly as roundworms) from other helminths. The phylum Nematoda is among the largest of the animal phyla. Approximately 15,000 species have been named; however, it has been estimated that if all the species were scientifically described, the number would be closer to 500,000. Nematodes occur as free-living forms in the sea, fresh water, and soil, or as parasites of plants, animals, and humans. Hookworms and threadworms infest the gastrointestinal tract. Filariae are found in the lymphatic tissues. The guinea worm and Onchocerca affect connective tissue. Some nematodes (e.g., threadworms) are transmitted from host to host by the ingestion of eggs; others (e.g., Wuchereria) by the bite of a blood-sucking insect. Related categories    • HEALTH AND DISEASE    • ZOOLOGY Also on this site: Encyclopedia of Alternative Energy & Sustainable Living Encyclopedia of History Transport Concepts & Designs (partner site) BACK TO TOP