The lion's mane jellyfish is one of the largest jellyfish in the world.

The lion's mane jellyfish, also known as the giant lion's mane jellyfish, is a large jellyfish of the family Cyaneidae, mainly distributed in the Arctic Ocean and cold waters such as the North Atlantic and North Pacific. It gets its name because the dense, trailing tentacles beneath its bell resemble a lion's mane, making it a highly recognizable large planktonic animal in the ocean.

It is known for its enormous size; its bell diameter can often exceed one meter, and its tentacles can stretch to over ten meters or even longer when extended, so it is often considered one of the largest known jellyfish. The bell is mostly reddish-brown or orange-yellow, with the shade varying according to the individual's size and age, and the tentacles are covered with fine stinging cells.

The lion's mane jellyfish prefers cold-water environments and mostly drifts with ocean currents in near-surface waters. It is a carnivorous animal, relying on its stinging cells to paralyze and capture plankton, small fish and shrimp, and even other smaller jellyfish; after the prey is delivered to the oral arms, it is gradually digested and absorbed, occupying an important position in the food chain of cold seas.

It should be noted that the stinging cells of the lion's mane jellyfish are toxic to humans; after being stung, reactions such as stinging pain, redness and swelling usually appear, and it is generally not fatal, but people with sensitive constitutions should treat it promptly and seek medical attention, and must never touch it directly with their hands. Affected by wind, waves and ocean currents, they are occasionally washed onto beaches, so extra caution is needed when active along northern coasts.