Jellyfish are probably some of the most bizarre, beautiful, and often annoying creatures of the ocean. My good friend and former roommate Courtney could sit, stare and sketch jellyfish while at the Aquarium for hours, and even has jellyfish tattoos on the side of her stomach. Because of her appreciation for these pretty critters, I dedicate this post to her.
Why are jellyfish so alluring despite their tendency to have painful greetings? Well, look at them. How many creatures do you know that are translucent and near transparent? Different jellyfish species are between 95 and 98% water, whereas us humans are a little over 60%. Another reason jellyfish are so pretty is probably because they are radically symmetrical, meaning both halves from the central axis mirror each other. Jellyfish do not have a brain, a respiratory system (breathing), a circulatory system (cycling materials, especially blood, around our body), or even an excretory system (filtering nutrients and getting rid of waste). Because of this, jellyfish actually go to the bathroom out of the same "hole" they take in food from.
Jellyfish don't even look like they should be alive with all their simplicities. Yet jellyfish, as a species, are older than the dinosaurs, and there's even thought to be an immortal jellyfish found (Thank you Christopher for showing me the article!). With so little inside their bodies, jellyfish must be pretty amazing at what they do in order to stay alive so long. Their "senses" consist of a neural net, "eyespots" detecting light from dark, and chemo-sensory pits that help detect prey. Jellyfish never stop growing, unlike us who typically tend to stop growing in high school after we've gone through sexual maturity. Without a respiratory system, jellyfish simply "breathe" in oxygen through their membrane-like skin. In order to swim, they use "jet propulsion" by taking in water through a muscular bell and shooting it out behind them. They aren't even fish, technically, because they don't have gills. Many scientists prefer to call them "sea jellies."
With no real internal organs or complex systems, you may wonder how jellyfish even reproduce. Well, jellyfish can reproduce sexually and asexually. Jellyfish are either born male or female, and each sex develops its eggs or sperm inside a pouch on their body. One fine day, the jellyfish will "throw up" their goods, and the goods pass from the stomach through the mouth. The eggs that stick to the lady jelly's mouth will be fertilized. The fertilized eggs become a planula, which is carried around ocean currents for quite some time until it is able to attach onto a surface and develop into a polyp. The polyp undergoes budding, which is like an asexual development of another polyp, and these polyps lead to the medusa stage. Some polyps actually split open through fission in order to become a medusa. Pretty weird, huh?
One jellyfish in particular, the box jellyfish, is known as the sea wasp. This little baby has 64 anuses (I'm serious) and 24 eyes, though they still can't really see. The box jellyfish is by far the most poisonous jellyfish, and it's sting can kill in 3 minutes. The amount of venom in one box jellyfish can kill up to 60 people. What's even more scary is that it can move at 2 meters.... per second. That means it would be pretty difficult to be stung and get back to shore. Thus, more people die from jellyfish attacks than sharks. Australians are well aware of this jellyfish, and they actually go swimming in regions where the jellyfish are located with women's pantyhose covering their arms and legs because the tentacles' little poison dart like nematocysts won't penetrate it. Additionally, their tentacles are near invisible and are pretty easy to get tangled up inside, which is why jellyfish are so good at finding prey despite the fact that most of them use ocean currents to get around. Think about how incredible it is that something so simple in form is not only alive, but has so much power and potential. Here we are, humans fully capable of adapting for life on every continent and have all kinds of fancy organs and systems, but some little thing that poops out of its mouth can cause us to stop breathing. It's pretty humbling to say the least.
Now that I've terrified you, know that most jellyfish species are not capable of killing you. A lot of jellyfish don't actually cause pain to humans because their stings are so subtle. Most of the ones who can noticeably sting you will not actually kill you, though they might make you whiney, and jellyfish are never aggressive. Jellyfish are just another one of the creatures on this planet that are beyond anything we could dream up, and reminds us that fact can indeed be strange than fiction.