1. Jellyfish Might be Even Older Than Dinosaurs
Fossils of jellyfish are difficult to find because jellyfish do not have any bones! However, those that have been uncovered are extremely old. For example, many well-preserved jellyfish fossils were discovered in Utah that date back to 505 million years ago when it was covered by ocean waters. Many scientists believe that jellyfish may have lived even earlier, however, possibly up to 700 million years ago!
2. Jellyfish Are Not Fish
Although we call them “jelly-fish,” these unique ocean-dwellers are not actually fish at all! Whereas fish have backbones, jellyfish are invertebrates without scales, fins, or gills. “Jellyfish” (or sea jellies) describes several groups of water-dwelling, gelatinous animals like “true” jellyfish, comb jellyfish, box jellyfish, and sometimes siphonophores. Jellyfish move through the ocean by pulsating their bells and absorb oxygen through their thin membranes.
3. Jellyfish Comes in All Shapes and Sizes
There are countless varieties of jellyfish in the ocean. “True Jellyfish”, for example, have the iconic “jellyfish” shape, with an umbrella-shaped bell on top, and tentacles and/or oral arms streaming out below. Tentacles are straight and slender, but they can be short or long. Oral arms are much thicker than tentacles and can be short, long, bushy, embellished, or branching. True jellyfish cannot control their movements very well, so they rely instead on the ocean’s current for transportation. Box Jellyfish, on the other hand, look like gummy boxes with long streaming ribbons. They have one or more stinging tentacles that hang from the four corners of their cube-shaped bell. Box jellyfish have much more control than true jellyfish and can swim through the water much quicker. One of the largest jellyfish species is the Lion’s Mane Jellyfish (Cyanea capillata). The bulk of this large jellyfish comes from the enormous, hair-like tentacles that flow from its bell like a lion’s mane. The largest lion jellyfish ever recorded had a bell that was 7 feet in diameter, and tentacles that were 120 feet long! The smallest jellyfish species is the Common Kingslayer. Measuring less than half an inch, this tiny jelly is smaller than a fingernail! However, don’t let its small size fool you. Common kingslayers are one of the most dangerous jellyfish, and one of the most venomous animals on earth.
4. Jellyfish Do Not Have Hearts or Brains
The body of a jellyfish is made of 95% water and does not have any of the organs usually found in animals. In fact, a jellyfish lacks a brain, heart, and stomach, as well as bones, blood, intestines, lungs, and eyes! With so little making up the body of a jellyfish, how does this curious creature live and breathe? The body of a jellyfish has two main layers: the epidermis layer on the outside, and the gastrodermis layer on the inside. In between these two layers there is a watery, gelatinous material called mesoglea. Jellyfish also have a very simple digestive cavity that works like a combined stomach and intestine. And here’s a somewhat disgusting jellyfish fact: jellyfish have a mouth in the middle of their bodies that allows them both to eat food as well as to expel waste. In addition, jellyfish also have a sensitive “nerve net”. This is a unique nervous system that helps them to perceive light, smell, and respond to other external sensory activity. Since they do not have lungs or gills, jellyfish absorb oxygen by diffusion through their thin, gelatinous membranes.
5. Only One Species of Jellyfish Has Eyes
Here’s a rather strange jellyfish fact: the Box Jellyfish is the only jellyfish species that has eyes. In fact, these jellies have 24 eyes! Box jellyfish have clusters of eyes arranged around all four sides of their cube-shaped bell. Because of the unique placement of their eyes, the box jellyfish is one of the few animals in the world that can view its surroundings in 360 degrees.
6. Some Jellyfish Change Color and Glow in the Dark
There are several species of jellyfish that can change the color of their bodies, and some of them can even glow in the dark! The Moon Jellyfish (Aurelia aurita), for example, typically has a pale, translucent bell that looks like a full moon. However, depending on what the jellyfish eats, its bell can change to purple, pink, white, or blue. Many other jellyfish species are bioluminescent, which means that they can produce their own light due to chemical reactions inside of their bodies. Scientists believe that around 50% of jellyfish species are bioluminescent and can produce their own light. These jellies mostly live in the darkness of the deep sea, where their bioluminescence helps them to attract prey, and to defend them from predators. The Crystal Jellyfish (Aequorea Victoria) is probably the most famous bioluminescent jellyfish. Normally this jelly is crystal clear and can be difficult to see. However, when it is threatened or disturbed, the crystal jellyfish emits green and blue light. Another intriguing jelly, the Atolla or Alarm Jellyfish (Atolla wyvillei) has a red body that flashes when it is attacked by a predator.
7. Not All Jellyfish Are Dangerous
A surprising jellyfish fact is that, contrary to popular belief, not all jellyfish are actually dangerous. Jellyfish are carnivores that use their venomous tentacles to hunt plankton, fish, and crustaceans. However, most jellyfish species are not dangerous to humans, and typically only cause discomfort or pain. In fact, there are some jellyfish species that are harmless to humans, like moon jellies (Aurelia aurita), Blue Buttons (Porpita porpita), and Mushroom Cap Jellyfish (Rhopilema Verrilli). These three species can still sting, but their venom is mild and usually only causes some skin irritation or a rash. The most venomous jellyfish is the Sea Wasp (Chironex fleckeri). This is a species of box jellyfish with a painful and potent venom that has been known to kill humans within a matter of minutes. Sea wasps have 60-foot-long stinging tentacles that can grow up to 10 feet long. However, for a sea wasp to sting you, it needs to have direct contact with the surface of your skin. Some swimmers claim that wearing nylon pantyhose will keep these killer jellies from stinging you. But be careful, because even a dead jellyfish can still sting! After a storm it is common to find many dead jellyfish scattered along the ocean shore. In New Hampshire several broken tentacles from a lion’s mane jellyfish washed up on shore and stung nearly 100 people on the beach!
8. Jellyfish Can Reproduce Together—or By Themselves
Although there are both male and female jellyfish, these curious sea creatures can reproduce sexually with a partner, as well as asexually by themselves. Adult jellyfish, called medusae, reproduce sexually. Male jellies release sperm and females release eggs into the water, and once fertilized, the eggs grow into tiny jellyfish larvae. These tiny jellyfish larvae eventually attach themselves to smooth surfaces and become polyps. Jellyfish polyps reproduce asexually by budding or splitting into several new jellyfish.
9. A Group of Jellyfish is Called a Bloom
When jellyfish gather together in groups, they are called a “smack” or a “bloom.” These blooms can contain millions of jellyfish at a time! While many marine animals are suffering greatly because of climate change, large blooms of jellyfish are becoming more common. Unfortunately, the populations of jellyfish predators like sea turtles are declining because of overfishing and human-caused pollution. Because of this, jellyfish are reproducing in large numbers. Blooms of jellyfish can disrupt power plants that use water from the sea and destroy fisheries.
10. Jellyfish Can Regenerate and Possibly Live Forever
On of the most incredible jellyfish facts is their shocking immortality. Not only can jellyfish reproduce on their own, they can heal themselves, regenerate, and even grow new body parts! Some jellies can also modify their existing parts to restore order and balance to a lop-sided body. Scientists observed that after losing two of its arms, a young moon jellyfish simply reorganized its remaining parts in order to restore its lost symmetry. Then there is the Immortal Jellyfish (Turritopsis dohrnii). This jellyfish gets its name from its unique ability to live forever! When an immortal jellyfish becomes too stressed, it will revert from its adult medusa stage and become a baby polyp again. By using this process of “transdifferentiation,” the immortal jellyfish avoids aging out and dying by beginning its life cycle over from the beginning again.
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