Jellyfish are marine invertebrates belonging to the Scyphozoa class, and in turn the phylum Cnidaria.
The body of an adult jellyfish is composed of a bell-shaped, jellylike substance enclosing its internal structure, from which the creature's tentacles suspend.
Each tentacle is covered with stinging cells (cnidocytes) that can stun or kill other animals: most jellyfish use them to secure prey or as a defense mechanism.
Others, such as Rhizostomae, do not have tentacles at all..
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