The true jellyfish has one of the more
interesting life cycles of animals.
- This starts off when male and female jellyfish spawn. Many times this is synchronized with the moon and the changing seasons (akin to that of its cousins, the corals). The eggs can be fertilized either in the water itself, or under the bell of the female jellyfish. When released to the free water, both the sperm and the eggs are considered plankton (and a vital source of food for some animals)
- The eggs eventually hatch into jelly larvae. These small zooloplankton (plankton coming from the Greek planktos meaning wandering - similar to that of planet) swim around on cilia waiting to bump into something firm. Realize that this is sometimes a very long journey for some species of jellyfish that live in the open ocean, thousands of miles from the coast. Seaweed and floating debris will do just fine.
- Once the larva are attached to a surface they grow into polyps that resemble corals, sea anemones, or hydra with tentacles. Like the animals which it resemble, the polyps can reproduce asexually by budding a new polyp from its side.
- As the polyp matures (living typically for a few months to several years), it will undergo strobilation - dividing itself into a series of flat segments (dozens). These segments loosen and fall off to form ephyrae.
- The ephyrae is a juvenile form of the adult medusa (jellyfish). Though still small enough to be considered plankton it jus just a matter of food (as an ephyrae it eats smaller plankton) and time before they grow large enough to become sexualy mature and thus an adult.
- The adult jellyfish typically lives for about 2-6 months. Cause of death is typically either being eaten (the sunfish and sea turtles being the primary predators), rough water or being washed ashore.
- One species (the Turritopsis nutricula) is capable of returning to the polyp stage (#3) after becoming a mature adult.
Realize that this cycle is that of a true jellyfish (class Scyphozoa)
such as the Moon Jelly, the Lion's Mane, Sea Nettle and Sea Wasp. Not all members of the phylum Cnidaria are jellyfish (and not at all jellyfish are true jellyfish, such as those of Cubozoa). The phylum Cnidaria includes sea anemones, corals, sea pens and hydra along with jellyfish. Each of these have their own life-cycle.
http://www.tnaqua.org/Special/JellyIntro.html
http://www.aquarium.org/
http://www.aqua.org/