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Jellyfish Reproduction

Everything You Always Wanted to Know About Jellyfish Reproduction, But Were Afraid to Ask

Have you ever wondered about jellyfish reproduction?  The birds do it; the bees do it; and, of course, the jellyfish do it as well.  But how do they do it?

If you’ve ever looked at a jellyfish you know that it’s not altogether clear how such a creature would reproduce.  They don’t have the usual set of reproductive organs.  They don’t even have backbones!  Clearly, these creatures work in ways that are far different from us.  So how does jellyfish reproduction work?

Well, what you will find is that the Jellyfish has one of the strangest reproductive cycles around. Let’s get started.

Do jellyfish have genders? Are there boy and girl jellyfish?

That’s a good question, after all there doesn’t seem to be any male or female sex organs hanging from the jellyfishes semitransparent bodies.  Jellyfish do, however, have distinct sexes. That is, the male jellyfish does produce sperm and the female eggs.

How does jellyfish sex actually work?

Here’s where jellyfish reproduction starts to get strange.  The sperm and eggs are stored in the jellyfish’s tummy.  Then when the time is right and the male jellyfish sense females around the spit out their sperm forming a cloud of sperm.  These sperm swim into the mouth of the female jellyfish who allow their eggs to be fertilized there.

And then they have little jellyfish babies?

No.  The females spit out the fertilized eggs that now develop into what scientists call planula.

Planula? What is planula?

Planula are these little creatures that look a little bit like fleshy light bulb shaped balloons, with little waving cilia, hair-like legs, that make them resemble caterpillars.  A hole opens on top of these little guys and they float to the bottom of the ocean where they seek out a place to strategically lodge themselves for the next phase of transformation.

So this is when they become jellyfish?

No, not yet.  While attached they transform into polyps and then reproduce asexually creating more polyps and growing until they become strobila. While they are polyps, they look like vases attached to the ocean floor.   As they transform into strobila, they slowly grow stringy extensions, like tiny tentacles. They sit on the bottom of the ocean eating and growing, in a similar way to anemones.

How long does that take? A few weeks?

Years sometimes.  They will just sit there and sit there, like a caterpillar in its cocoon waiting for the moment when it will release and float up into the ocean. Just before they begin to release like this they develop stratified rings around its cone like surface.

And that’s when it becomes a jellyfish?

Nope.  The rings that developed become more pronounced and begin to break off.  This intermediate creature is an ephyra. In this phase, it still looks a little like a jelly starfish.  But as it grows in the ocean, it evolves into its fully mature form. 

This fully mature phase is called the medusa, like the Greek mythological figure that turned people to stone.  It has a diaphanous dome and a spongy looking interior with a floating bouquet of tentacles that trail it and help propel it through the water.

These beautiful creatures are one of the most soothing to watch as they gently float and hover in the ocean water.  There movements are so graceful it is hard to believe they are even real. Given how peaceful they look its surprising how much change they have undergone to acquire this serene state.

So that’s the quirky world of jellyfish reproduction. And you thought your cousin had a strange sex-life.



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