Typical Nematodes - Roundworms
A soybean cyst nematode and egg
picture taken with a scanning
electron microscope of a plant parasitic nematode.
Galls (swollen regions) formed on vegetable roots
of infestation by parasitic nematodes
Meloidogyne incognita- a plant parasite
500X, in the process of penetrating a tomato root. The worm will
establish a feeding site once inside, which causes a nutrient-robbing
Other Nematodes - Roundworms
I can't bring
myself to call them "cool" like I have on other pages
in this section as many are just too gross
Typically 15 to 35cm in length, these
are parasitic of humans
Elephantiasis, a result of a parasitic infection of filarial
nematodes. The nematodes that cause this are microscopic
and cause a blockage of the lymphatic system and so fluid retention
with tissue and skin thickening. The legs and genitals are particularly
affected, the scrotum can swell to the size of a basketball in some
Ancylostoma caninum - a hookworm
attached to the
intestine of a dog, though species of hookworm infect other mammals
including humans. The name comes from them being bent over at the
head end so forming a hook.
Nematode infestation in the vomit of a cat
(yes I know
it's gruesome, but nematodes are like that)
used permission of Kalumet at de.wikipedia
GNU Free Documentation License, Version 1.2
Kingdom - Animalia
- Roundworms get their name from their round cross section
- Long thread-like bodies
- Usually very small to microscopic, some parasitic members
however may be a metre long
- Simple tube-like gut with a mouth and anus
- No circulatory system, gas exchange and excretion are by
diffusion across the body wall
- There is very little superficial difference between nematode
species, they all look pretty much like larger or smaller, somewhat
fatter or skinnier versions of each other
- Sexual reproduction, sexes separate, no asexual reproduction.
Males are usually smaller than the females, the females of some
species can deposit over 100,000 eggs per day.
Phylum - Nematodes
The group includes:
Nematodes 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 f