Underwater footage shot by underwater drillers of a jellyfish near their well sparks sea monster rumours

They can stop the world's biggest warships, cripple power stations and kill humans with a single sting but jellyfish are not about to take over the world and turn our oceans to slime, as some reports have claimed.

Portuguese man-of-war sighted at Mediterranean beaches

The jet-black rubber RIB was running flat out in the February night. We were sweeping past the Mongstad oil refinery at the Norwegian west-coast, just south of Gulen Dive Resort, and the clock was approaching midnight. Apart from the lights in the distance, the visibility was zero, and we were navigating solely on GPS, chart plotter and radar. The speed of 35 knots produced a howling wind, although the sea was completely calm. There was no moon, which was perfect for what we had in mind—an encounter with the alien of the deep, the crown jelly, Periphylla periphylla.

What? Animals in the sea armed with missiles? And thousands of them? Yes, you’ve read correctly. No, sea lions or dolphins have not been stealing Tomahawk missiles from any of the American navy bases. But did you know that jellyfishes, sea anemones and corals contain thousands of “miniature missiles” to kill prey and sting intruders? We will look at bit closer at this missile battery mechanism here.

Probably about 90 percent of deep-sea animals are bioluminescent. Some jellies use bioluminescence as a defense, i.e. they glow when disturbed in order to light up their predators, making their attackers vulnerable to even larger animals. A few deep-sea fishes and squids have glowing organs that look like lures, but even these animals have never been observed actually using their glowing organs to capture prey.

Jellyfish-like creatures may play major role in the marine carbon transport system

When the Mnemiopsis jellyfish suddenly appeared in the Baltic Sea, people feared the worst for our ecosystem.