The Lion's Mane Jellyfish (Cyanea capillata) is the largest known species of jellyfish. Its range is confined to cold, boreal waters of the Arctic, northern Atlantic, and northern Pacific Oceans, seldom found farther south than 42°N latitude.
Although capable of attaining a bell diameter of 2.5 metres (8.2 ft), these jellyfish can greatly vary in size, those found in lower latitudes are much smaller than their far northern counterparts with bells about 50 centimetres (20 in) in diameter. The tentacles of larger specimens may trail as long as 30 metres (98 ft) or more. These extremely sticky tentacles are grouped into eight clusters, each cluster containing over 100 tentacles,arranged in a series of rows.
The bell is divided into eight lobes, giving it the appearance of an eight-pointed star. An ostentatiously tangled arrangement of colorful arms emanates from the centre of the bell, much shorter than the silvery, thin tentacles which emanate from the bell's subumbrella.
Size also dictates coloration—larger specimens are a vivid crimson to dark purple while smaller specimens grade to a lighter orange or tan. These jellyfish are named for their showy, trailing tentacles reminiscent of a lion's mane.
A coldwater species, this jellyfish cannot cope with warmer waters. The jellyfish are pelagic for most of their lives but tend to settle in shallow, sheltered bays towards the end of their one-year lifespan. In the open ocean, lion's mane jellyfish act as floating oases for certain species, such as shrimp, medusafish, butterfish, harvestfish, and juvenile prowfish, providing both a reliable source of food and protection from predators.
Predators of the lion's mane jellyfish include seabirds, larger fish, other jellyfish species, and sea turtles. The jellyfish themselves feed mostly on zooplankton, small fish, ctenophores, and moon jellies.