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Animal
forms like plant life thrive in water providing
conditions are right. Among the higher forms of animal
life found in water are fish, amphibians (turtles and
frogs), mollusks (snails and shellfish) and anthropoids
(lobsters, crabs, water insects, water mites and others)
Our
concern here is with those lower forms of animal life in
water. Again, some are helpful to man as scavengers;
others are injurious as possible sources of infection.
Worms
There
are three types of worms found in water. For the most
part they dwell in the bed of material at the bottom of
lakes and streams. There they do important work as
scavengers.
The
rotifers are the only organisms in this category at or
near the surface. They live primarily in stagnant fresh
water.
The
eggs and larvae of various intestinal worms found in man
and warm-blooded animals pollute the water at times.
They do not generally cause widespread infection for
several reasons: they are relatively few in number and
are so large they can be filtered out of water with
comparative ease.
Protozoa
Another
basic classification in the animal kingdom is that a
group of microscopic animals known as protozoa. These
one-celled organisms live mainly in water at or near the
surface or at great depth in the oceans.
Many
live as parasites in the bodies of men and animals. Like
other organisms, protozoa can be classed as helpful or
injurious. Sometimes drinking water becomes infested
with certain protozoa that are not disease producing.
When present, they give the water a fishy taste and
odor.
Some
protozoa are aerobic, that is, they exist only where
free oxygen is available. Some exist where no free
oxygen is available. Others can be either aerobic or
anaerobic.
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