World Jellyfish Day

 Today is World Jellyfish Day!

Jellyfish are invertebrate marine animals. Most of them are free-swimming critters, but some do get anchored to the seabed by stalks. Jellyfish are known for their body shapes. Their main bodies resemble an open umbrella (it's called a bell), and their trailing tentacles. 

Jellyfish can be found in waters all over the world. Most of them live in saltwater environments, but there are some that live in fresh water. 

Jellyfish are among the oldest multi-organed animals. Fossil records have indicated that they have been around for 500 million years, possibly 700 million. Speaking of fossilization, jellyfish fossils are rare because they have no hard body parts like bones or teeth. 

Jellyfish's bodies are comprised mainly of water, and most species have no brain, lungs, heart, or central nervous system. Well, they don't really need them. Jellyfish breathe by oxygen diffusing through their epidermis, which also contains their non-centralized "nerve nets".

Do jellyfish eat? Of course they do! They're carnivorous, believe it or not. Their diets include plankton, small fish, crustaceans, fish eggs, larva, and some jellyfish even eat other jellyfish. There are omnivorous jellyfish, like the Aglaura hemistoma. The Lion's Mane Jellyfish is arguably the longest animal on Earth, as their tentacles can reach up to 120 feet in length, but that is actually pretty rare.

Jellyfish reproduction is actually rather unique among the animal kingdom as they involve a mix of sexual and asexual reproduction. Adult jellyfish release reproductive materials into the water, where it's fertilized and collected by the female. These eggs become larvae that eventually became polyps. The polyp eventually buds out the jellyfish, which then enters the medusa stage, aka the form that most think of when they see a jellyfish. 

Jellyfish lifespans aren't completely known, but one species may be effectively immortal as it can revert to a polyp stage, a phenomenon that only has been observed in a lab setting. 

Jellyfish tend to be preyed on the most by...other jellyfish. However, sharks, tuna, and swordfish, sea turtles, and penguins have been known to feed on them. Certain land animals like birds can feed on washed-up jellyfish as well. People also can eat jellyfish. In fact, they're delicacies in some Asian countries like Japan, Korea, and China. 

Jellyfish are also known for their stings. That's because their tentacles have lots of nematocysts, special cells dedicated to injecting venom into anything that touches them.  However, most species' stings are not fatal to humans. Some are, so be careful around them. Some species of fish live among jellyfish tentacles and help lure prey into them. 

Jellyfish can be nuisances in other ways. They're capable of overcoming an oceanic ecosystem, and they can damage fishing nets in large numbers. They've even been known to disrupt power plants. 

So yeah, jellyfish are pretty fascinating critters! Thanks for reading this blog entry! If you liked it, show it off! Take care of yourselves and each other! If you like what I write and want to give this blog some additional support, please make a donation to my Ko-Fi! See you next time!