All jellyfish are invertebrates, which means that they lack backbones. The rest of their anatomy is quite simple, including a primitive nervous system that is capable of detecting heat, light, food and vibrations. Since jellyfish lack eyes and ears, these nerves are their primary method of navigating the ocean.
Though jellyfish come in many colors, their skin is always translucent and their internal organs, which are suspended in a jelly-like substance, can be seen through the outer layer of epidermis. The jellyfish's mouth is located on the bottom of its body, surrounded by several tentacles that help it catch and guide food.