Jellyfish come in a dazzling array of colors, shapes, and sizes, drifting through every ocean, from the surface to the deepest of the deep seas, and are even found in freshwater locations. These ancient creatures, also called sea jellies (they are not, technically, fish), are so otherworldly and luminous that it is no wonder they are often compared to mythical shapeshifters. Some are so delicate that they shatter with the smallest disturbance to the water, while the tenacity of others means they can withstand almost any temperature, any salinity, starvation, and even being dismembered. And some are truly biologically immortal.