The lion’s mane jelly is the largest sea jelly among the over 200 species that make up the class of the true jellies, Scyphozoa. The genus name, Cyanea, is derived from the Greek ‘kyanos” which means dark blue. The first species described in the genus was dark blue. The Latin ‘capillus’ means hair and presumably describes this jelly’s many tentacles. The common name, lion’s mane, describes the perceived resemblance of the tentacles and their typical color to that of a lion’s mane. Because of their appearance, these jellies have been described as a mop hiding under a dinner plate. 

Named for its flowing, hair-like tentacles that resemble a lion’s mane, this jelly drifts through cold and temperate waters of the Arctic, Atlantic, Pacific, North Sea and Baltic Sea. It is striking both for its massive size and bright colors of pink, reddish-gold, or brownish-violet. Beneath its bell hangs over 1,000 tentacles, each of which contains stinging cells called nematocysts. 

These special stinging cells help the jellyfish snag a snack! The lion’s mane jellyfish will position itself above fish, spread out its tentacles, then slowly sink down towards its prey, catching it in its tentacle net and stunning it with its nematocysts. While their sting is powerful and may be painful to humans, they do not intentionally sting people. Unusual for jellyfish, they are known to come together in shoals, which can sometimes be a kilometer (0.6 miles) long!

The animal is generally found within the first 20 metres (65 feet) of the ocean’s surface, where it feeds on zooplankton, small fishes, and ctenophores (comb jellies) as well as other jellyfish. The lion’s mane jellyfish captures its prey by delivering a sting loaded with neurotoxins from the nematocysts (stinging cells) on its tentacles. After the prey has become immobilized, specialized tentacles called oral arms transport the prey to its mouth. The lion’s mane jellyfish is preyed upon by sea turtles (which do not seem to be affected by the neurotoxins), birds, and larger fishes as well as other jellyfish.