What Are the Stages of a Jellyfish?

Fertilization

• A male jellyfish releases sperm that floats into the undulating female jellyfish's mouth. The sperm is dispersed into her gonads. The gonads develop the sperm and hold on to it until eggs are produced. The eggs grow and become released to the water though the female's mouth.

Planula

• The planula is the first developmental stage. Planulae are free-swimming and oval. The planula stage lasts for a few days. The planulae rise to the surface of the ocean and are transported by currents. They eventually sink before they enter the polyp stage.

Polyp

• The planulae affix themselves to a surface underwater and don't move. The attachment positions their mouths and tentacles facing outward. New polyps form and emerge, and the planulae congregate on the same surface. All all connected, and nourishment is dispersed among them by tubes. This stage lasts for years as the colony grows.

Ephyra

• Polyps continue to grow in a communal grouping called a hydroid. All the polyps affixed to an underwater object begin to form horizontal grooves on their bodies. The grooves become more pronounced. This is when the ephyra detach themselves and turn into swimming jellyfish. They are extremely small, and again float to the surface as they did as planulae.

Medusa

• Medusa is the adult form of jellyfish. Full development has occurred, with the formation of the bell that is the circular body. Arms and tentacles are grown, as well as gonads that are visible through their transparency. The continued development at this point in the life of the jellyfish results in increased size. A jellyfish can grow as large as 14 feet.