Chlorohydra viridissima
Copyright 2002, Microbus
Hydras are tiny animals,
which are closely related to jellyfish. Green Hydras live in
fresh water, such as streams, rivers, lakes, and ponds. They
are very common. A Green Hydra can grow up
to 30 millimeters long, but usually they are less than 15
mm. Green Hydra are found in
shallow water, where they attach themselves to plants,
stones, twigs, or other objects. Unlike their jellyfish
cousins, they don't like to float around. The body of a Green Hydra
is long and skinny. Just like jellyfish they have stinging
tentacles. One hydra can have anywhere from four to twelve
tentacles. Each tentacle has tiny bumps, called nematocysts.
The nematocysts release a material that paralyzes another
animal. Hydras use their nematocysts to capture prey, and
for protection. Bio Images UK, Malcom
Storey Green Hydras use a sticky
body fluid at their base to attach to an object in a place
where there is a lot of food swimming by. Sometimes they
attach to the surface of the water and hang down. Prey of Green Hydras
include aquatic insects, crustaceans (such as water fleas
and scuds), flatworms, aquatic worms, fish fry, and other
small creatures in the water. They also eat a certain type
of algae, called Chlorella, which is what makes
hydras green. Chlorella stays alive inside the hydra.
Since algae is a plant, it makes its own food. The hydra
lets the Chlorella make food for it. The way Green Hydras
reproduce (make more hydras) is by budding. Budding starts
with a small bump on a hydra's body. The bump continues to
grow until there is a stalk. Next, the new stalk grows
tentacles. When it is ready, the new hydra pinches itself
off from its parent. Bio Images UK / Malcom
Storey The picture above shows a
hydra bud forming. To the right is another picture, with two
buds on an adult Green Hydra. With the right
temperature, and a good food supply, a healthy Green Hydra
can make a new bud every three or four days. The population (amount of
hydras in one place at one time) is at its greatest in late
Spring and early Summer. Predators of hydras
include flatworms, crustaceans, and aquatic
insects. Sometimes Green Hydras
attach themselves to mussel shells. If a hydra needs to move
(perhaps it's not getting enough food), it can detach itself
and move like an inchworm. Copyright 1975, 2001
Andrew A. Skolnick
