Jellyfish are simple, successful and, occasionally, deadly creatures. The Australian box jellyfish has enough toxin in each of its tentacles to kill 60 people. Some jellyfish create spectacular blooms when fields of polyps, their stationary life stage, simultaneously bud off into free-floating medusae. These blooms are blamed for the deaths of swimmers, clogged fishing nets and power plant intakes, and in certain parts of the world, like Japan, they appear to be on the rise.
But these problems are associated with only a subset of the creatures we call "jellyfish" – a catch all term for an amazingly diverse group of organisms. It includes corals, true jellies and others with stinging cells, as well as the stingless comb jellies, which swim using tiny hairs, called cilia.
What they also are is beautiful, as the following images attest.