How they live?

Most Cnidarians present these two forms during their life, a sessile or immobile form (called a polyp) and a free form (medusa form). When they are polyps, they are fixed to the substrate and can live both singly and in colonies. The mouth is located at the top. When they are jellyfish, the mouth is in the center of the animal and points downwards and is surrounded by the tentacles.

Where are they distributed?

In tropical seas and cold Arctic waters.

What do they feed on?

Zooplankton, small crustaceans, small fish and other jellyfish.

How do they reproduce?

Reproduction can be sexual and asexual. Asexual reproduction occurs in the sessile form (polyps) and sexual reproduction occurs in the medusa form. The objective of asexual reproduction is to grow in groups, while sexual reproduction is to generate genetic biodiversity among jellyfish species.

Jellyfish stings are caused by the activation of nematocysts, which are stinging structures. The discharge mechanism of a nematocyst is produced by the action of mechanical and chemical stimuli. Water enters the nematocyst, and pushes the tube that is coiled inside it to the outside of the capsule. This barbed tube enters the prey’s tissues 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: burning sensation, irritation and sometimes death. Once the nematocyst is used, it regenerates again.

How they feed?

The tentacles are found surrounding the edge of its body and use it as a mesh to capture food: zooplankton and also small jellyfish. When they have caught something, through vibrating movements they send it to the oral arms and these to the mouth.