A jellyfish smaller than a pinky fingernail has spread to every ocean on Earth, almost certainly by hitchhiking inside ship ballast water tanks, and researchers have now found genetically identical individuals worldwide — raising the question of whether one animal has been reincarnating across the globe for centuries

A jellyfish smaller than a pinky fingernail has spread to every ocean on Earth, almost certainly by hitchhiking inside ship ballast water tanks, and researchers have now found genetically identical individuals worldwide — raising the question of whether one animal has been reincarnating across the globe for centuries

Hold your little finger up and look at the nail. A fully grown Turritopsis dohrnii would fit on it with room to spare. The bell is about 4.5 millimeters across, transparent, with a bright red stomach at the center and a fringe of up to 90 hair-thin tentacles. In the water it is almost invisible. This is the animal the world has come to call the immortal jellyfish. It was first described from the Mediterranean in the 1880s, and for a century nobo…