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 don’t seem to be any male or female sex organs hanging from the jellyfish’s 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 which allows their eggs to be fertilized there.
And then they have little jellyfish babies?
No. The females spit out the fertilized eggs, which now turn into what scientists call a 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, and 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. Their movements are so graceful it is hard to believe they are even real. Given how peaceful they look it’s 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.
Medusa Jellyfish
The medusa jellyfish is the final, adult jellyfish and the most well-known and recognizable one of the species. In the marine world, jellyfish are one of the most beautiful creatures with all of their peculiar colors and designs they have a whimsical look to them. As simple as they look underwater, they have a very complex lifecycle(another interesting article – Blobfish Underwater). There are four cycles in a jellyfish’s life planula, polyp, ephyra, and medusa.
The medusa jellyfish is known as a fully developed, bell-shaped creature with thick arms that hang alongside its mouth and tentacles all over the margins of its body. It has a stomach and gut in a very small stomach cavity on the underneath part of the bell. The inner layer of the medusa jellyfish is formed with a mesogea gelatin substance. The gonads are developed during this stage of life and are visual through their translucent bodies.
The jellyfish prior to this period in its life started out as a very tiny embryo. The embryo transforms into what is called a swimming planula and remains at this stage for a few days where it floats to the surface and rides the current of the water for a while. After it floats for a bit, it finally sinks in the water and then enters the polyp stage. During this part of the jellyfish’s life, it sticks itself to a hard surface and several of them use feeding tubes among them to ensure they’re all receiving equal nutrients. This stage can last for many years and the colony has the ability to grow quite large. The polyps start eventually developing horizontal grooves. As the groove matures they are set free, leave the colony, and turn into a medusa jellyfish. They only have the ability to reproduce once when they reach this stage in their life.
Medusa jellyfish were first discovered about 650 million years ago. They are found in every ocean and can even survive in fresh water. A group of jellyfish is called a swarm and sometimes a bloom and can be extremely intimidating of course dangerous to encounter. They do not have a respiratory system because their skin is so thin that their bodies are actually oxygenated by diffusion. They don’t have brains but instead function by using a network of nerves. The medusa jellyfish is made up of over 90% water and not only can they be fascinating patterns and vibrant colors, but they can also be much larger than most people realize.
The box jellyfish has venom that makes it the absolute most deadly creature in the entire animal kingdom. Since 1954 almost 6,000 deaths have been recorded due to contact with them. The tentacles have harpoon-style needles that are used to inject venom.
Largest medusa
The largest medusa jellyfish is the lion’s mane. It is one of the longest animals with the bell having a diameter of almost 8 feet and the tentacles can reach 120 feet.
Medusa are considered carnivorous
Medusa are labeled as carnivores. They are essentially drifters that feed off of small fish or traces of dead animals floating in the water. They also consume traces of zooplankton that becomes caught in their tentacles. There are over 200 species of jellyfish and each one is more mysterious-looking than the last. If you are ever stung by a jellyfish it is imperative that you remove the tentacles immediately. The venom can only reach your skin through the needles. The stings from a medusa jellyfish can cause you to collapse or go into shock and often are the cause of death.
