Jellyfish Facts

Jellyfish Facts
Jellyfish is a freely swimming marine animal which belongs to the phylum Cnidaria. There are more than 350 species of jellyfish that can be found in all oceans of the world. Some species can also live in the fresh water. Jellyfish can be spotted on different depths, from the surface to the very deep ocean water.
Interesting Jellyfish Facts:
Jellyfish vary in size greatly. Smallest species (Irukandji) can be barely seen with human eye (sized as a pinhead), while the largest (Lion's mane) can be almost 8 feet wide in diameter.
Jellyfish has a bell or umbrella shaped body with tentacles whose length and number depend on the species.
Jellyfish can be transparent or vividly colored.
Jellyfish is made of gelatinous mass which contains 95 percent of water.
Jellyfish is very simple organism. It does not have brain, bones, head or heart. Some species can detect the light using the primitive and simple form of light-sensitive organs called ocelli. They are anatomically much simpler than eyes of higher animals.
Jellyfish are one of the oldest organisms on the planet. They appeared on the Earth before dinosaurs. Scientists believe that jellyfish exist between 500 and 700 million years.
Jellyfish are highly adaptable organisms. There are four hundred zones in the oceans (known as deadly zones) where only jellyfish can survive.
Jellyfish are the most famous for their ability to sting. Certain species of jellyfish produce very painful and sometimes even deadly sting. Deadly sea wasp belongs to the group of the box jellyfish. That is the most dangerous jellyfish in the ocean which contains enough toxin to kill 60 people. Sting of the sea wasp is very painful and may result in death if medical help is not available.
Even dead jellyfish is able to sting. Jellyfish kill more people than sharks each year.
Jellyfish does not attack humans primarily. They use stinging cells as a weapon to catch the prey in the water. Stinging cells are called nematocysts.
Jellyfish eat different types of food: phytoplankton (algae floating in the superficial water), copepods, fish eggs, larvae of different species and other jellyfish.
Jellyfish are not strong swimmers; they depend on the sea current most of the time. When sea current gather huge number of jellyfish at the same area - the group of hundreds or thousands animals are known as swarms.
Jellyfish "bloom" is another phenomenon associated with huge number of jellyfish which results from increased reproduction when the food sources are abundant and other environmental conditions are optimal. Water with low concentration of oxygen and increased temperature of the sea facilitates blooming of the jellyfish.
Jellyfish development is divided in two phases: mobile and stationary. After male and female reproductive cells fuse together, fertilized egg develop into polyp. Polyp is a sedentary organism (attached to the rocks on the bottom of the sea) which produces large number of little jellyfish that quickly grow into adult and mobile jellyfish. Polyp is a result of sexual reproduction and jellyfish babies of asexual.
Lifespan of the jellyfish ranges from several hours to several months, depending on the species.

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