Jellyfish are cnidarians, word that comes from Greek and means nettle (Cnida-), as this group of animals in their tentacles have stinging cells (cnidocitos) employing both to hunt prey and for their own defense.

How they live?
Most cnidarians have two ways during his life, a sessile or immobile form (called polyps) and free (jellyfish form). When polyps are fixed on the substrate and can live either alone or in colonies. The mouth is at the top. When they are jellyfish, the mouth is in the middle of the animal and pointing down and around the tentacles.

Where are they distributed?
They are distributed in tropical seas and cold Arctic waters.

What do they eat?
They eat zooplankton, small crustaceans, small fish and other jellyfish.

How do they reproduce?
Reproduction may be sexual and asexual. Asexual reproduction is given as sessile (polyps) and sexual in the way jellyfish. The purpose of asexual reproduction is to grow in groups, while sexual is to generate genetic diversity among species of jellyfish.

Jellyfish stings are caused by the activation of nematocysts that are urticopunzantes structures. The discharge of a nematocyst occurs by the action of mechanical and chemical stimuli. Water enters the nematocyst, and pushes the tube is wound inside to the outside of the capsule. That tube with thorns enters the tissues of the prey and injects a paralyzing toxin. In humans, depending on the type of toxin (which in turn depends on the type of jellyfish) it can produce a burning sensation, irritation and sometimes death. Once the nematocyst is used, it becomes regenerate.

How they feed?
The tentacles are found around the edge of your body and use it as a mesh to capture food: zooplankton and small jellyfish. When they have caught something, by vibratory movements send him to the oral arms and these mouth.