Hydra are tiny members of Hydrozoa, a group of Cnidarians that live predominantly in freshwater. They live their life in a sessile way, attached to the substrate. When food comes along, their tentacles eject nematocysts or stinging cells. This releases a neurotoxin to paralyze their tiny prey and the proceed to ingest that prey into their mouth by a feeding reflex. If Hydra remain well-fed, they can sometimes form one or many buds. These buds are a form of asexual reproduction for this animal. If the bud should break off, it can do a somersault--like motion until it settles down into a suitable location. It will then grow independently. Sometimes, the buds remain attached and a colony will form.
Hydra is a tiny animal from belonging to the phylum Cnidaria and the class Hydrozoa, that lives in ponds and lakes. Animals like jellyfish, sea anemones, and corals also belong to the same class of animals.
The hydra, which has one of the simplest structures among all the many-celled animals, is shaped like a thin cylinder about as thick as heavy thread and is 6 to 13 millimetres long. One end of its body attaches to sticks, stones, and water plants. The other end contains the mouth, which is surrounded by five to seven tentacles that act like tiny arms. The hydra usually stays attached in one place for some time. But it can move about by slowly along the bottom of the pond or lake, or by drifting beneath the water's surface film.
Buds in hydras are small, knob like growths that appear on their body and enable hydras to reproduce. These buds develop from time to time, and as they develop grow tentacles. When the buds are fully developed, they break off and live as independent hydras.