Green Hydra

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

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Video (Long download, approx 1 minute on T1)
Mark Moran
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Relationships in Nature: 

PREY
PREDATORS
SHELTER
OTHER

Water Flea

Flatworm

Common Cattail

Eastern Lamp Mussel SP

Copepod

Crayfish

Arrow Arum

Chlorella Algae C

Scud

Copepod

Hydrilla

Asian Tiger Mosquito

Water Flea

Greater Bladderwort

Northern Caddis Fly

Large Diving Beetle

Common Duckweed

Eastern Mosquitofish

Green Darner

Green Algae

Creek Chub

Ebony Jewelwing

Common Reed

Bluegill

Eastern Dobsonfly

Pickerelweed

Largemouth Bass

Predatory Nematode

Long-leaf Pondweed

Freshwater Leech

Marsh Bulrush

Aquatic Worm

Lizard's Tail

Green Darner

Yellow Pond Lily

Ebony Jewelwing

Wild Rice

Chlorella Algae

Relationship to Humans:

Green Hydras are helpful since they control populations of insects (including mosquitoes). They must have good water with lots of oxygen to live, so when we can't find them, it's a sign that water may not be healthy.

 
SCIENTIFIC CLASSIFICATION

KINGDOM
Animal
PHYLUM
Cnidaria
CLASS
Hydrozoa
ORDER
Hydroida
FAMILY
Hydridae
GENUS
Chlorohydra
SPECIES
Chlorohydra viridissima

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