They can sting you and it hurts! Trust me, I know...
Yes
First of all, the man-of-war is not a true jellyfish. Its body is filled with air. To be a jellyfish the "bag" of their body has to be filled with water. Also a box jellyfish is more dangerous. The box jellyfish is the most dangerous jellyfish in the world.
The box jellyfish is lethally dangerous if you have been stung over more than a few square centimeters of skin.
Their venom.
Clear
Most jellyfish are not dangerous. The Man o' War has the ability to do some painful damage to your skin, but it is not a true jellyfish . . .
Yes, both dangerous and friendly :-)
Some jellyfish stings are dangerous to humans.
A jellyfish has tentacles which can sting by injecting a toxin. Jellyfish can be extremely dangerous, despite being a very primitive type of organism with no skeletal system.
IDK.Box jellyfish, Portuguese Man o war, Sea nettle, Earacounge (Ear-a-con-g). IDK the rest
Yes, it is. It has been proven numerous times in several experiments that swimming with jellyfish is extremely dangerous and can for a fact cause serious injuries and/or death. Trying this is highly discouraged for your own safety.
Crystal Jellyfish mainly feed on humans, whales and another large mammals in the ocean. The Crystal Jellyfish is one of if not the most dangerous organism in the ocean. they can kill a whale within 43 seconds. They are found throughout the entire world which makes them even more dangerous.