Marine Biology

A look at the Lifecycle of a Jellyfish



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Jellyfish have been surfing the ocean currents for over 650 million years, constantly reproducing and adapting to survive in our changing seas.

There are several types of jellyfish - possibly more than two thousand, according to marine experts - but almost all of them follow the same steps of the life cycle.

In order for a jellyfish to be conceived, male jellyfish release sperm into the water. The sperm swims into the mouth of a female. From there, the sperm fertilize the eggs and eventually form an embryo - just like any typical process of reproduction.

After conception, there are five basic stages in the life cycle of a jellyfish.

1. A jellyfish embryo doesn't automatically turn into a baby jellyfish; instead, it becomes what's called a planula. A planula can swim, but not as gracefully as a jellyfish. It uses tiny cilia (hair-like extensions from it's body) to propel itself to the ocean floor, where it will attach itself to a hard, immobile object.

2. Once it's attached to a rock, shell, or other solid object, it begins to transform into a polyp. Polyps can survive for several years by catching and eating tiny sea creatures. These little polyps become capable of asexual reproduction - what that means is that growths from the walls of the polyp's body form and split off - and they've got all the makings to be their own separate polyp; this process is called budding.

3. As it grows, grooves in the polyp's body start to develop. When this happens, the polyp looks like a stack of discs on top of one another. Eventually, the grooves get so deep that they actually separate the body - and each piece is finally a baby jellyfish!

4. Baby jellyfish move through adolescence and become adults, just like every living creature does. As adults, they are capable of sexual reproduction and free to create tiny planula of their own.

Jellyfish are cnidarians, which means they're not actually a fish at all! 98% of a jellyfish's body is made of water - their thin (and sometimes transparent) skin holds a sticky, water-based goo inside. They have no bones or brains - but that doesn't stop their instinct for survival; some jellyfish stings can be fatal to humans.

5. Most jellyfish only live for about a year. Generally, those who live less than a year die at the flippers of hungry sea turtles. Once a jellyfish dies, it is either eaten by other sea creatures or decomposes on the ocean floor - either way, it's helping the sea's delicate ecosystem.

While jellyfish are simple creatures, their intricate process of procreation and birth are fascinating. Their short life span doesn't decrease their population, either - every day, new planula and polyp buds are developing on the ocean floor.

The next time you wonder what's lurking beneath the surface of the sea, don't forget the 2,000 different kinds of jellyfish and how they got there.

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