Nematodes or roundworms make up an animal phylum all of their own - the Nematoda. To put that into context, humans belong to one tiny branch of the phylum Chordata, which includes every other animal with a backbone from frogs to birds to primates. Nematodes are colourless, have no legs or segments, and many are difficult to see without a magnifying glass. Specialised knowledge is needed to tell one type of nematode from another.
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