Jellyfish are soft-bodied marine animals that belong to a group called Cnidarians. Cnidarians include animals such as sea anemones and corals. Unlike fish, mammals, or reptiles, jellyfish do not have a backbone. Because they lack a backbone, they are classified as invertebrates. Invertebrates make up the majority of animal life on Earth, and jellyfish are among the most ancient of these animals.
Scientifically, most jellyfish belong to a class known as Scyphozoa. This classification places them within the phylum Cnidaria. The defining feature of cnidarians is the presence of specialized stinging cells called cnidocytes. These cells contain tiny structures that can release a sting. This adaptation helps jellyfish capture food and defend themselves from predators.