Nematoda

The roundworms, a large phylum that includes many of the helminths parasitic in humans and a far greater number of plant-parasitic and free-living soil and aquatic nonparasitic species. For practical purposes, the parasitic nematodes may be placed in two groups, based on their adult habitat in the human body : 1) the intestinal roundworms ( e.g., the genera Ascaris, Trichuris, Ancylostoma, Necator, Strongyloides, Enterobius, and Trichinella); and 2) the filarial roundworms of the blood, lymphatic tissues, and viscera ( e.g., the genera Wuchereria, Mansonella, Loa, Onchocerca, and Dracunculus). [nemat- + G. eidos, form]

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Nem·a·to·da .nem-ə-'tō-də n pl a phylum related to the Aschelminthes and comprising elongated cylindrical worms without an epithelial coelomic lining, with dorsal and ventral nerve cords, and with lateral excretory ducts that are parasites of humans, animals, or plants or free-living dwellers in soil or water and are known as roundworms, eelworms, or nematodes

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Nem·a·to·da (nem″ə-toґdə) [Gr. nēma thread + eidos form] the roundworms, a class of the phylum Aschelminthes, tapered cylindrical helminths, of which many species are parasites. They are characterized by longitudinally oriented muscles and by a triradiate esophagus. In some systems of classification, they are considered to be a separate phylum. Sometimes called Nemathelminthes, or a class under that phylum.