Life cycle of a Jellyfish

More Than Just a Medusa

The most recognized image of a jellyfish is that of the adult jellyfish, with its bell-shaped body and long tentacles. But this image is just one of several stages in the life cycle of a jellyfish which include:

• egg and sperm
• planula larva
• scyphistoma (polyp)
• strobilating scyphistomata (polyp hydroid colony)
• ephyra
• medusa

Jellyfish experience alternation of generations in which one generation (medussa) reproduces sexually and the next (scyphistomae) reproduces asexually. The medusa form is the dominant form.

Egg and Sperm

Jellyfish reproduce sexually so adult jellyfish are either male or female. Male jellyfish release sperm into the water and the sperm then swims into the mouth of the female jellyfish (located on the underside of the bell of the medusa) where the eggs are fertilzed.
The fertilized eggs begin their development either inside the female or in brood pouches located on the oral arms.

Planula Larva

After the fertilized eggs have undergone embryonic develoment, they leave the mouth or brood pouch as free-swimming planula larva. The planula larva is a short-lived stage in the jellyfish's life cycle.

Scyphistoma (Polyp)

The planula larva eventually settles to the bottom where it attaches itself to a hard surface and transforms into a scyphistomata (or polyp). This polyp stage in the jellyfish life cycle is a sessile stage, so called because the polyp is stationary and not free-swimming.

Strobilating Scyphistomata (Polyp Hyrdroid Colony)

The polyp develops into a strobilating scyphistomata (also called a polyp hydroid colony) that is linked together by feeding tubes. The polyp hydroid colony, like the originating polyp, is sessile (that is, it remains attached to the hard surface and is not free-swimming).

Ephyra and Medusa

The polyp hydroid colony reproduce asexually to bud off tiny free-swimming jellyfish (called ephyra). The ephyra grow in size and become the adult (medusa) form of jellyfish.