Jellyfish
Jellyfish are soft bodied, free-swimming sea animals, usually with tentacles that can deliver a nasty sting.
In the medusa stage of their life cycle, most jellyfish are free-swimming creatures that can propel themselves through the water by pulsing their “bells”.
Jellyfish are usually meat-eaters, and feed on plankton, small fish, and crustaceans. Their main method of hunting is to trail their tentacles behind their bodies and wait for prey to drift into contact with them. The tentacles will then sting the prey, stunning or killing it and allowing the jellyfish to drag it toward its mouth for consumption.
Jellyfish have a complicated life cycle. The eggs hatch into larva, which then search for a place to anchor themselves, at which point they become polyps. The polyp will then grow and create “buds”, which are segments of the polyp that will separate and become free floating organisms. These buds will then float through the water, growing and eventually forming into the medusa stage, which is when they become the creatures most recognize as “jellyfish”.
The name “jellyfish” is often applied to a wide range of sea dwelling animals with soft bodies in the subphylum Medusozoa. Specifically, the “medusa” phase of the animal’s life cycle is what is commonly identified as a jellyfish. In this phase, the animal usually has an umbrella shaped main body (called a “bell”) with tentacles trailing beneath that contain stinging cells used for capturing prey.
Since they comprise such a large and wide-ranging group of marine creatures, jellyfish may come in many different sizes, shapes and colors, though they are often at least partially translucent (meaning their bodies are somewhat see-through). The smallest jellyfish can be about one millimeter long, while the largest species may have a bell measuring over six feet across, with tentacles trailing over one hundred feet behind them.
It is believed that jellyfish have been around for a very long time, possibly more than 500 million years. The term “jellyfish” has been used to describe these creatures since the late 1700s, although it is not accurate, since these creatures are not actually fish.
Jellyfish stings can be dangerous to humans. Some species only produce irritation from a sting. Others, like the box jellyfish, can be deadly to humans.
There are more than 2,000 different types of jellyfish known, though there may be many hundreds of thousands of species yet to be discovered. While some species of jellyfish are endangered, certain human activities that affect the environment are having the opposite effect – causing jellyfish populations to explode and increase as their natural predators suffer harm to their populations.
Changes in climate, increased pollution, and overfishing have all led to spikes in jellyfish population. These jellyfish blooms create swarms that can be dangerous to swimmers and damage fishing nets and other equipment.
References
https://en.wikipedia.org/wiki/Jellyfish
https://www.worldatlas.com/articles/how-many-species-of-jellyfish-are-there.html
https://www.weforum.org/agenda/2019/01/how-an-explosion-of-jellyfish-is-wreaking-havoc/
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