What, exactly, IS a jellyfish? Easily recognized by their almost-abstract form and often trailing long, flowing, sometimes electric or lit-up tentacles, jellyfish exhibit a kind of otherworldly beauty that has fascinated the human world for centuries. While some believe these creatures to be dangerous (and some are), most are only mildly harmful if touched or startled by the stray limb of a human swimming.
Jellyfish are part of a group called Cnidarians, named after the Greek word for "sea nettle." Cnidarians are marine creatures characterized by having jelly-like bodies and radial symmetry (as opposed to bilateral symmetry).
Another main characteristic of the unique form of the jellyfish is the presence of "cnidocytes" on their tentacles. Cnidocytes are cells on the jellyfish tentacle that actually explode when stimulated by prey (or in some cases, potential predators).