Jellies have an elementary nervous system, shaped like a net, throughout their bodies that can detect, light, smell and other stimuli. They cannot see or hear, however, and they never sleep. Jellies are comprised of about 95% water. In contrast, humans are about 65% water.
Off the Oregon Coast, sea nettle populations are increasing due to a reduction in predators, such as sea turtles and jelly-eating fish. Carnivorous themselves, their sting paralyzes their prey of other sea jellies, zooplankton and copepods.