How to know if a jellyfish is poisonous?

The more massive jellyfish would be more dangerous than the smaller version because of its size producing more cnidocysts. However, all jellyfish contain some poison. Cnidaria is named after their poison producing structures. Some jellyfish are poisonous, but many are not. Jellyfish have thousands of stinging cells on each tentacle. These cells are barbed and have a poisonous sac attached.

When you come in contact with the tentacles, thousands of these cells dig into your skin and release the poison. Most jellyfish venom is neurotoxic, meaning it attacks your nervous system. Jellyfish venom is one of the known most deadly toxins on Earth. Some carry poisonous venom in their tentacles as a method of self-defense against predators.