Jellyfish are coelenterates which spend most of their lives as free-floating bodies with drift the current. They can only actively move a limited amount by contracting their bell-shaped hood. Because they cannot swim against the current, they are categorized as zooplankton. A jellyfish is a simple animal, 98% of it consisting of water. All jellyfish have stinging cells, but only a few species can penetrate human skin. When these stinging cells touch you, it feels like you came into contact with a bunch of stinging nettles.