While the term "jellyfish" can be a bit misleading, as it encompasses a wide variety of organisms, all true jellyfish belong to the class Scyphozoa within the phylum Cnidaria.

Cnidarians are a diverse group of aquatic animals that share certain characteristics, including:

* Radial symmetry: Their body parts are arranged around a central axis.

* Tentacles: These are armed with stinging cells called nematocysts used for defense and capturing prey.

* Two distinct body forms: A polyp (sessile) and a medusa (free-swimming).

Jellyfish, specifically, are the medusa form of certain cnidarians.