Animal Spotlight: Lion’s Mane Jellyfish


  • Kingdom: Animalia
  • Phylum: Cnidaria
  • Class: Scyphozoa
  • Order: Semaeostomeae
  • Family: Cyaneidae
  • Genus: Cyanea
  • Species: capillata
  • Bell Diameter: up to 6.5 ft (2 m)
  • Tentacle Length: up to 100 ft (30 m)
  • Maximum weight: over 1 ton
  • Average Lifespan: 1 year

The lion’s mane jellyfish is one of the largest jellyfish in the world. It gains its common name from its characteristic mass of long, thin, hair-like tentacles found hanging from the underside of the bell-shaped body.

This jellyfish has a global distribution, although it is mostly found in the northern hemisphere in the North Atlantic, North Pacific, and North Sea. They can also be found in Australia and are especially prevalent near the east coast of Britain.

Despite being found globally, the lion’s mane jellyfish is a pelagic species and only found in open ocean. It is not present in brackish and shallow waters as it requires areas with higher salinity.

Physical Description:

The lion jellyfish is a simple organism, having only two tissue layers (diploblastic). Its smooth, saucer-shaped bell is round, radially symmetric. It is also relatively flat and consists of eight lobes. Its color is usually dark yellow, brown, or red in color, concentrated in the center and thinning out towards the edge. Despite its potentially large size, it is uncommon to find them because the lion’s mane jellyfish reaches their full size at the end of each summer, when they are out in the open waters.

Photographer: Getty

The mouth’s situated on the bell’s underside, surrounded by tentacles that are divided into eight clusters of between 70 and 150. There are also four thick, frilled, folded ‘oral arms’, where are shorter than the tentacles and are a dark red or red-brown. A juvenile lion’s mane jellyfish has pale pink, yellow or colourless oral arms, which become dark red as the individual ages.

In each of the lion’s mane jellyfish’ tentacles are nematocysts, barbs filled with venom. Each nematocysts contain a threat tube, which can fire venom through the end when stimulated. If a human gets stung, this venom can cause painful, long-lasting blisters and irritation to the victim. Muscular cramps as well as respiratory and heart problems are also possible in susceptible individuals. But for the most part, it is relatively harmless.


The lion’s mane jellyfish and its larvae are predators. They prey on zooplankton, small fishes, moon jellyfish, comb jellies, and other jellyfish species. It is known to catch prey with the powerful stings on its tentacles.


As a jellyfish, they possess no means of locomotion. Though their slow pulsations do weakly drive them forwards, they are at the mercy of the waves to travel great distances. Most will “swim” solo, but large swarms occasionally occur when storms and tides are prevalent.

On average, they live for about one year, during which four life stages: larva, polyp, ephyra, medusa.

Like other jellyfish, lion’s mane jellyfish are capable of both sexual reproduction in the medusa stage and asexual reproduction in the polyp stage. When they do breed via external fertilization, it is usually around March to early May.

The resulting larvae will then settle on the seabed, after a several days being carried by the female in its tentacle, and a small polyp, only a few centimeters across, will begin to grow. The polyps begin to reproduce asexually, creating stacks of small creatures called ephyra.

Eventually, the individual ephyrae break off to grow into the medusa stage and become full grown jellyfish. Small medusae are most abundant between April and May, mostly seen at the surface of the water. Mature individuals are seen between June and September.

Conservation and Threats:

The lion’s mane jellyfish not not yet been assessed by the International Union for the Conservation of Nature, but it is not thought to be threatened. Its primary predator, the leatherback turtle, relies heavily on the jellyfish to survive and eats them whole before they have matured. However, since the leatherback turtle populations are so low, no specific preventative measures need to be taken to reduce the chance of extinction. Human threats, on the other hand, including oil spills and ocean trash still can be fatal to these organisms.

In fact, some scientists believe that their population may be booming. Scientific research has suggested that jellyfish actually thrive in areas that are affected by human activity. Overfishing, climate change, and rising global sea temperatures have helped promote more frequent jellyfish swarms while reducing their main predators and competitors. These factors have created a favorable environment for this species, and few threats are known to the lion’s mane jellyfish or other jellies.

Interesting Facts:

  • The lion’s mane jellyfish is the largest jellyfish in the Atlantic Ocean
  • Like all jellies, the lion’s mane jellyfish is 95% water
  • It has no brain, blood, or nervous system
  • The lion’s mane jellyfish is often bioluminescent and can emit its own light
  • It can grow up to 120 feet long, bigger than a blue whale
  • Detached tentacles still retain their stinging power, though it loses effectiveness over time
  • While normally deadly, lion’s mane jellyfish stings don’t have much of an effect on the fish of the Caranx genus, which actively seek out the lion’s mane jellyfish and hover near their tentacles for protection.

References + For More References:

Lion’s mane jellyfish (Cyanea capillata)

10 Facts About the Lion’s Mane Jellyfish

Lion’s Mane Jellyfish

The Largest Jellyfish

15 Facts About the Lion’s Mane Jellyfish

Lions Mane Jellyfish

Giant Lion’s Mane Jellyfish

Cyanea capillata: The Enormous Lion’s Mane Jelly

Cyanea capillata: Lion’s mane

Lion’s mane jellyfish


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