Four others are carnivores or omnivores. They range

Four of every five multicellular animals on the
planet are nematodes. They occupy any niche that provides an available source
of organic carbon in marine, freshwater and terrestrial environments; they are
the planet’s most abundant metazoa. Nematodes are an evolutionarily successful
group of organisms. In soil, some nematodes feed on higher plants, some on
fungi or bacteria; others are carnivores or omnivores. They range in
reproductive potential from explosive opportunists to conservative survivalists.
The phylum Nematoda comprises the classes Secernentea and Adenophorea. The
Secernentea are almost exclusively terrestrial, only rarely being freshwater or
marine, whereas the Adenophorea occupy niches in all three habitats. Almost 20,000
nematode species have been described and millions of nematodes can occupy 1 m2
of soil. There can be 50 different species in a handful of soil and a 100-ml
core of soil yields sufficient individuals for reliable analysis. Routine analyses
of nematode fauna provide a basis for environmental management, remediation and
conservation decisions. Most
importantly, nematodes have variable responses to stress factors; some species
are extremely sensitive to pollutants and others extremely tolerant. It is difficult, and perhaps unimportant, to
calculate how many species are present when determining the biodiversity of an
area. Recent research indicates that simple analyses of in situ nematode
faunae at family level provide a wealth of information on the nature of
decomposition pathways and soil nutrient status. The analyses also indicate
effects of agricultural practices and contaminants on the functioning of the
soil food web. As a useful index of
bioindicators in ecotoxicological diagnosis, the prospect of soil nematode
application was of potential. Evidence
continues to grow to show that their community structures can help to track global
warming and, from a retrospective point of view, their global distributions may
even reflect the processes of continental drift and their biochemistry, the
history of the Earth’s chemosphere.


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