1. Hydra Notes

2. Classification
Kingdom: Animal Phylum: Cnidaria (meaning “hollow gut”) Body Structure: thin, hollow cylinders with 5-7 tentacles extending from the mouth Color: Tan, Grey, Green, Brown Size: 6-13 millimeters (0.2 to 0.5 inches) – can stretch and contract their bodies Hydra are one of the simplest multicellular organisms.

3. Anatomy Hydra have no circulatory systems, heart, or blood vessels.
Their bodies are only 2 cell-layers thick so oxygen diffuses (or drifts) into areas of the cells that are low in oxygen.
They have no skin, but the outer layer of cells protects them.
They do not have a stomach, but they do have an inner layer of cells that secretes enzymes that digest food.

4. Movement and Habitat
They do not have a central nervous system to control movement, but they do have a “nerve net”.
Through the “nerve net”, impulses that control muscular contractions are carried.
These contractions allow Hydra to expand, contract, and move.
Hydra spend much of their time attached to a surface, but when they move they float or travel by doing somersaults.
Hydra live in freshwater.

5. Reproduction Hydra can reproduce in 3 ways:
The most common form of reproduction for Hydra is budding – a form of asexual reproduction.
A small growth, or bud, forms on the Hydra body through a series of cell divisions.
The bud develops tentacles, breaks away, and can live independently.

6. Hydra can also reproduce by regeneration.
Hydra can reproduce sexually.
Hydra develop sex organs and reproduce sexually when the temperature gets cooler.
They wait until the temperature gets cooler because the eggs can survive in cooler conditions, but the parents cannot.

7. Poisonous Hydra feed on small organisms, such as Daphnia.
Some of the outer layer of cells of the Hydra is made of nematocysts – stinging structures.
When an organism, like Daphnia, brushes against Hydra’s tentacles, the nematocysts shoot out threads.
These threads pierce the prey and release a paralyzing poison.

8. Other nematocysts release threads that surround the prey and hold it tight. The tentacles then move the prey towards the Hydra’s mouth and force it into the digestive cavity.