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Nematodes:
Pervading the Earth and Linking All Life

J. G. Baldwin
Department of Nematology, University of California, 1455 Boyce Hall, Riverside, CA 92521
S. A. Nadler
Department of Nematology, University of California, 588 Hutchinson Hall, Davis, CA 95616-8668
D. H. Wall
College of Natural Resources, Colorado State University, Fort Collins, CO 80523

Abundance of Nematodes

The phylum Nematoda (Nemata), known commonly as roundworms, contains the most abundant, common, and genetically diverse multicellular organisms (Lambshead 1993; Platt and Warwick 1983). Usually, these organisms are invisible to all but a few specialized scientists because most are essentially microscopic and transparent. More than 85 years ago, Cobb (1914) eloquently noted that “if all the matter in the universe except the nematodes were swept away, our world would still be dimly recognizable, and if, as disembodied spirits, we could then investigate it, we should find its mountains, hills, vales, rivers, lakes, and oceans represented by a film of nematodes.” “So little do we know of this vast multitude of soil-inhabiting nematodes that the first spadeful of earth we lift is practically certain to contain kinds never seen before”, and 'There exists . . .a greater disproportion between the known and the unknown than exists in almost any other class of organisms.” With respect to Cobb's characterization of our knowledge of nematode diversity, relatively little has changed during the last 85 years. Somewhere between 500,000 and more than 100,000,000 nematode species are believed to exist on Earth (Lambshead 1993), but habitats certain to be richest in new species are mostly unexplored, and fewer than 25,000 species have been described (Andrássy 1992; Platt and Warwick 1983).

Diverse morphological, physiological, and behavioral adaptations allow nematodes to pervade nearly every habitat, but most habitat adaptations cross formal taxonomic boundaries, which arguably include two classes and 18 orders