Beacons of colorful whimsy in a dreary world, nudibranchs are nonetheless best observed from a safe distance or not at all. Those colors are a warning. Swim too close, and you'll be stung within an inch of your life. Not that they care. Whether you seize up and die or just keep your distance, as long as you're only looking, you're safe. (Photo by Pascal van de Vendel)
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