Lion's mane jellyfish

The lion's mane jellyfish (Cyanea capillata), also known as the giant jellyfish, arctic red jellyfish, or the hair jelly, is one of the largest known species of jellyfish. Its range is confined to cold, boreal waters of the Arctic, northern Atlantic, and northern Pacific Oceans. It is common in the English Channel, Irish Sea, North Sea, and in western Scandinavian waters south to Kattegat and Øresund. It may also drift into the southwestern part of the Baltic Sea (where it cannot breed due to the low salinity). Similar jellyfish – which may be the same species – are known to inhabit seas near Australia and New Zealand. The largest recorded specimen was measured off the coast of Massachusetts in 1865 and had a bell with a diameter of 7 ft and tentacles around 120 ft long. Lion's mane jellyfish have been observed below 42°N latitude for some time in the larger bays of the East Coast of the United States.

The lion's mane jellyfish uses its stinging tentacles to capture, pull in, and eat prey such as fish, zooplankton, sea creatures, and smaller jellyfish.

Taxonomy
The taxonomy of the Cyanea species is not fully agreed upon; some zoologists have suggested that all species within the genus should be treated as one. Two distinct taxa, however, occur together in at least the eastern North Atlantic, with the blue jellyfish (Cyanea lamarckii Péron & Lesueur, 1810) differing in color (blue, not red) and smaller size (10 - 20 cm diameter, rarely 35 cm). Populations in the western Pacific around Japan are sometimes distinguished as Cyanea nozakii, or as a subspecies, C. c. nozakii. In 2015, Russian researchers announced a possible sister species, Cyanea tzetlinii found in the White Sea.

Description
Lion's mane jellyfish (Cyanea capillata) are named for their showy, trailing tentacles reminiscent of a lion's mane. They can vary greatly in size: although capable of attaining a bell diameter of over 2 m, those found in lower latitudes are normally smaller than their far northern counterparts, with a bell about 50 cm in diameter. Furthermore, larger specimens are typically further offshore than smaller ones. Juveniles are lighter orange or tan, very young lion's manes are occasionally colorless and adults are red and start to darken as they age.

While most jellyfish have a circular bell, the bell of the Lion's Mane is divided into eight lobes, giving it the look of an eight-point star. Each lobe contains about 70 to 150 tentacles, arranged in four fairly distinct rows. Along the bell margin is a balance organ at each of the eight indentations between the lobes – the rhopalium – which helps the jellyfish orient itself. From the central mouth extend broad frilly oral arms with many stinging cells called Cnidocytes. Closer to its mouth, its total number of tentacles is around 1,200.

The long, thin tentacles which emanate from the bell's subumbrella have been characterised as “extremely sticky”; they also have stinging cells. The tentacles of larger specimens may trail as long as 30 m or more, with the tentacles of the longest known specimen measured at 120 ft in length, although it has been suggested that this specimen may actually have belonged to a different Cyanea species. This unusual length – longer than a blue whale – has earned it the status of one of the longest known animals in the world.

Behavior and reproduction
Lion's mane jellyfish remain mostly very near the surface, at no more than 20 m depth. Their slow pulsations weakly drive them forward, so they depend on ocean currents to travel great distances. The jellyfish are most often spotted during the late summer and autumn, when they have grown to a large size and the currents begin to sweep them to shore. Unlike most pelagic jellyfish, they are completely solitary and rarely travel in groups.

Like other jellyfish, lion's manes are capable of both sexual reproduction in the medusa stage and asexual reproduction in the polyp stage. Lion's mane jellyfish have four different stages in their year-long lifespan: a larval stage, a polyp stage, an ephyrae stage, and the medusa stage. The female jellyfish carries its fertilized eggs in a tentacle, where the eggs grow into larvae. When the larvae are old enough, the female deposits them on a hard surface, where the larvae soon grow into polyps. The polyps begin to reproduce asexually, creating stacks of small, immature medusae called ephyrae. The individual ephyrae break off from the stacks, where they eventually grow into the mature medusa stage to become full-grown jellyfish.

Sting and human contact
Human encounters with the jellyfish can cause temporary pain and localized redness. In normal circumstances, however, and in healthy individuals, the stings of the jellyfish are not known to be fatal; vinegar can be used to deactivate the nematocysts. If there is contact with a large number of tentacles, however, medical attention is recommended after exposure.

There may be a significant difference between touching a few tentacles with fingertips at a beach and accidentally swimming into the jellyfish. The initial sensation is more strange than painful and feels like swimming into warmer and somewhat effervescent water. Some minor pain will soon follow. Normally, there is no real danger to humans (with the exception of people suffering from special allergies). But in cases when someone has been stung over large parts of their body by not just the longest tentacles but the entire jellyfish (including the inner tentacles, of which there are around 1,200 ), medical attention is recommended as systemic effects can be present. Although rare, severe stings in deep water can also cause panic followed by drowning.

In July 2010, around 150 beachgoers were stung by the remains of a broken-up lion's mane jellyfish along Wallis Sands State Beach in Rye, New Hampshire, US. Considering the size of the species, it is believed that this incident was caused by a single specimen.

In popular culture
A photograph widely distributed on the internet appears to show an anomalously large lion's mane dwarfing a nearby diver. The photo was subsequently shown to be a hoax.

On the television program QI, the show claimed that the longest animal in the world was the lion's mane jellyfish. This was later corrected – in 1864, a bootlace worm (Lineus longissimus) was found washed up on the coast of Fife, Great Britain, that was 180 ft long. This claim is, however, disputed because bootlace worms can easily stretch to several times their natural length, so it is possible the worm did not actually grow to be that length. If that is the case, the lion's mane jellyfish would indeed be the longest animal in the world.

The creature is referred to as the culprit in a short story entitled The Lion's Mane in The Case-Book of Sherlock Holmes by Sir Arthur Conan Doyle.

Predators
Seabirds, larger fish such as ocean sunfish, other jellyfish species, and most sea turtles will only attack juveniles or smaller specimens while a fully grown adult is incapable of being eaten, due to their massive size and the abundance of stinging tentacles they possess, although both adults and juveniles have been documented eaten by anemones. The leatherback sea turtle feeds almost exclusively on them in large quantities during the summer season around Eastern Canada.

Other sources

 * British Marine Life Study Society – C. capillata and C. lamarcki
 * Marine Life Information (UK)
 * Marine Biological Laboratory (Massachusetts)
 * Pacific Coast jellies