matodes are probably the commonest multicellular organism
that you've never heard of and have hardly ever seen. They occur
in all environments, in fresh and sea water, on land, in polar regions
and in deserts. They can be found in hot springs, high up mountains
and in the deepest oceans.
Most nematodes live in the "benthos" - sediments, whether
soil or aquatic sediments. A square metre of mud from an inshore
area near the coast of Holland was measured to contain over 4 million
nematodes. Good farm soil as well as containing a large number of
earthworms can also contain from several hundred million to several
billion nematodes per acre.
A single decomposing apple on an orchard floor has had 90,000
nematodes counted in it of several species and a single decomposing
fig around 50,000 of at least eight species.
Although there are so many free-living nematodes, they tend to
be microscopic and therefore unknown to all but the scientists who
study them. There are however a large number of nematodes that
are parasitic on a wide range of animals and plants, these are
rather better known than the free-living forms. These parasitic
forms have major economic and health influences in parts of the
world where they are found.
- Vinegar eels - tiny free living worms that can live
in vinegar or liquids that can become vinegary such as cider,
wine, beer etc.
- Caenorhabditis elegans - a 1mm long free living nematode
that has been used for many years (starting in 1974) as a "model
organism" for scientific research. At maturity all individuals
have exactly 959 cells. It was the first multicellular organism
to have its complete genome sequenced (in 1998), so leading
ultimately to the "Human Genome Project."
- Toxocara canis - the one that puppies are "wormed"
to remove and that can cause blindness in children if they come
into contact with animal faeces and are infected.
- Loa loa - the Africa eye worm
- Guinea worm
- Species that produce "filiariasis" in man -
What do nematodes eat?
Many free-living nematodes are carnivorous, they feed
on animals that are even smaller than they are including other nematodes.
Other free living nematodes feed on phytoplankton such as diatoms,
algae and fungi. Many terrestrial species feed on plant roots, penetrating
the cells and sucking out the contents. They are considered parasitic
in the way that fleas are parasitic on other animals, they can cause
great damage to the plants in this manner.
Species that live in sediments and other aquatic environments
ingesting particles of the substrate when they digest associated
bacteria and / or organic material.
Others feed more directly on dead organic material such as decomposing
plants and animals or dung where they may actually be eating the
bacteria or fungi that are feeding on the decomposing material
rather than being a decomposer directly.
The parasitic forms of nematodes show a great many variations
on the theme.
- Ectoparasite of plants - lives outside the plant
- Endoparasite of plants - lives and breeds inside
the plant having entered as a juvenile
- Saprophagous - juveniles and adults are free living,
juveniles enter invertebrate animal host and cause no harm,
but feed on dead tissues when the host dies.
- Zooparasitic juvenile stages only - juveniles
parasitize a host organism and then leave when it becomes
adult, the adult does not feed and may not have a
functioning gut. its job is reproduction only.
- Phytoparasitic juvenile, Zooparasitic adult - juvenile
lives as a plant parasite and is taken in by the animal host when it
feeds. The adult then parasitizes the adult and infects the
larvae of the host with juvenile worms which are then ready
to enter and parasitize the plant host again.
- Zooparasitic adult females only - young live in the
soil, males die after fertilizing females in the soil, pregnant
females then enter the animal host.
- ... and a whole range of other strategies with more than
one host to help the worms distribute themselves and complete
their life cycles
What eats nematodes?
Free living nematodes are themselves
prey for almost any 