Aquatic and Land Animal Diversity


How numerous are roundworms?

Roundworms, or nematodes, are members of the phylum Nematoda (from the Greek term nematos, meaning “thread”) and are numerous in two respects: 1) number of known and potential species; and 2) the total number of these organisms in a habitat. Approximately 12,000 species of nematodes have been named, but it has been estimated that if all species were known, the number would be closer to 500,000. Nematodes live in a variety of habitats ranging from the sea to soil. Six cubic inches (100 cubic centimeters) of soil may contain several thousand nematodes, a square yard (.85 square meters) of woodland or agricultural soil may contain several million of them, and good topsoil may contain billions per acre.


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