The jellyfish is instantly recognizable with its bell-shaped, pulsing body and its dangling tentacles. But this appearance is only one part of a jellyfish's life cycle. Most start as buds off polyps on the ocean floor or a coral reef.
The reproduction process starts when a male jellyfish releases sperm into the water near a female jellyfish, who takes it to fertilize the eggs she's holding in her mouth. Fertilized eggs grow into larvae called planulae. On release from the female jellyfish, these drift through the ocean until they land on a firm surface, such as coral, rock or even a crab shell. There they attach and grow into polyps, with short tentacles pointing up.
Polyps don't need additional fertilization to begin budding; they perform asexual reproduction. The polyps start growing branches out to the sides. As the branches get larger, they detach and drift down to attach to the surface beside the original polyp. This creates an exact replica of the first polyp. Both begin to create more buds, which can lead to a large colony of jellyfish polyps covering an area of the ocean floor. Once attached, they don't release from the surface; they just sit and eat and bud.
Not all polyps produce more polyps when they bud. Some begin to bud differently -- instead of branches growing outward, the top section begins to separate into structures with horizontal lines. Each of these buds matures into a tiny medusa jellyfish, which is the translucent bell shape most commonly recognized as a jellyfish. Because the medusa buds are created through asexual reproduction, all the buds from one polyp with produce jellyfish of the same gender.
Although what you typically think of as a jellyfish -- the medusa portion of the life cycle -- is the most commonly seen, it's the shortest part of the animal's life cycle. Polyps can live for up to five years, budding often. Free-swimming medusas, on the other hand, live for only a few months. Their main goal is to live long enough to reproduce and create more larvae that can become polyps that bud for years.