Jellyfish contain the power to sting someone, but other than this elementary defense mechanism, they are harmless, and in some respects beautiful, creatures. Jellyfish belong to the phylum Cnidaria, and they are invertebraes, or animals with no backbone. They contain a very simple nervous system. Their body contains a system of simple neurons that are capable of detecting food, light, warmth and vibration. Smell and taste are aided by chemoreceptors, which allow the jelly to detect odor and food.
Light receptors allow the jelly to distinguish light and dark, but no shapes or external dimension.
This system can be seen under their skin, which is translucent. They contain a thin outer layer of clear skin, and a gastrodermis, or an inner layer lining the stomach and inside cavity. The middle of the jellyfish is filled with the jelly, or mesoglea. Their mouth is typically underneath them as they move, and they contain a series of tentacles that help draw food inside them. The inside cavity is a stomach, digestive cavity, intestine and gullet all in one.