Page 80 - The Microworld Miracle

change of nourishment: While the worm feeds the bacteria, the bac-
teria produce food for the worm.
Another marine worm, Riftia pachyptila, needs bacteria for di-
gestion. This species of worm has no digestive system of its own.
It used to be thought that this invertebrate lacking a digestive
system absorbed organic substances dissolved in sea water by
means of its skin. However, it was soon realized that the surface ar-

ea of its skin is too small in proportion to its volume for it to possi-
bly feed in this way. In 1981 the astonishing discovery was made
that the worm actually fed in a normal way, but that its digestion
was actually performed by bacteria. The cooperation between the
worm and the bacteria is indeed most practical. The water the
worm takes in through its gills is rich in sulfur and oxygen, sub-
stances carried by its bloodstream to where the bacteria can make

organic compounds. The waste materials of metabolisms such as
substances containing nitrogen and carbon dioxide are reabsorbed
by bacteria and
turned into nutri-
ents.
The worm's
metabolic wastes,
such as carbon di-
THE MICROWORLD MIRACLE The worm species Riftia

pachyptila needs bacteria
to digest its food.

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