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. 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.
Lion’s mane jellyfish 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 (6 ft 7 in). Juveniles are lighter orange or tan, very young lion’s manes are occasionally colorless and adults are red and darken as they age. 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.
The largest recorded specimen was measured by Alexander Agassiz off the coast of Massachusetts in 1865 and had a bell with a diameter of 7 feet and tentacles around 120 ft long.
The bell of the lion’s mane jellyfish is scalloped into eight lobes (lappets), each lobe containing from 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. Closer to its mouth, its total number of tentacles is around 1,200.