A barrel jellyfish can loom over a diver, its bell broad as a patio table and its frilled arms trailing beneath it, yet the encounter is usually more nuisance than emergency. That feels backward. Size is not a venom scorecard: this animal is built to filter plankton and trap small prey, not to subdue a large mammal with a catastrophic dose. Its bulk is mostly water. The jellyfish uses nematocysts,...More