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.
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