Jellyfish Are Invertebrates
Invertebrate means an animal that does not have a spine. Jellyfish do not have any bones, ears, brain, heart, feet, or legs. However, they do have a very basic nervous system that has receptors to detect vibrations, light, and chemicals in their immediate surroundings. These receptors enable them to navigate through the water.
Instead of a mouth, jellyfish have a digestive tube that protrudes from its body, through which they feed. In some types of jellyfish, this tube is surrounded by curly tentacles that look like ribbons; these tentacles are known as mouth arms or oral arms. To breathe, jellyfish do not need lungs or gills, as the skin on their bodies is thin enough that they can breathe through it.